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THE  I 

LITERARY  AND  SCIENTIFIC 

CLASS  BOOK,  I 

i 

EMBRACING  THE  j 

LEADING  FACTS  AND  PRINCIPLES  OF  SCIENCE.  | 

XUttstratetf  i)S  ISnfltatJinirs, 

WITH    MANT    DIFFICULT     W0RB8    EXPLAINED    AT    THE    HEADS    OF   THK  | 

LKSSONS,  AND  QUESTIONS  ANNEXED  FOR  EXAMINATION  ',    DESIGNED  AS  'l 

KXERCISE3    FOR    THE  READING    AND    STUDY  OF  THE  HIGHER  CLAS5BS  ] 

SS  COUHON  SCHOOLS.  j 

SELECTED    FROM   THE 

'3 

REV.  JOHN  PLATTS'  \ 

aCUrars  an^  .Scicntliic  &am  JJooife, 

JlitfD  FROM  VARIOUS  OTHER  SOURCES,  AND  ADAPTED  TO  THE  WANTS  AKB  j 

CONDITION  OF  YOUTH  IN  THE  UNITED   STATES.  | 


By  LEVI  W.  LEONARD. 


tXXREOTYPED  BY  T.  H.  CARTER  &  CO.  BOSTOK. 

PUBLISHED  ^Y  J.  &J.  W.PRENTISS. 
1831. 


/ 

DISTRICT  OF  NEW-HAMPSHIRE,  to  wit  ; 

District  Clerk's  Office. 

Be  it  remembered,  t|iat  on  the  twelfth  clay  of  November,  A.  D. 
1825,  and  in  the  fiftieth  year  of  tlie  Independence  of  the  United 
States  of  America,  John  Prentiss  of  the  said  District,  has  deposited 
in  this  office  the  title  of  a  book,  thp  right  whej-eof  he  claims  as  pro- 
prietor, in  the  words  followin":,  to  wit : — 

"  The  LITERARY  AND  SCIENTIFIC  CLASS  BOOK,  embrac- 
ing the  leading  facts  and  principles  of  Science.  Illustrated  by  engrav- 
ings, with  many  difficult  words  explained  at  tlie  heads  of  the  lessons, 
and  questions  annexed  for  examination  ;  designed  as  exercises  for  the 
reading  and  study  of  the  higher  classes  in  common  schools.  Selected 
from  the  Rev.  John  Platts'  Literary  and  Scientific  Class  Book,  and 
from  various  other  sources,  and  adapted  to  the  wants  and  condition 
of  youth  in  tho  United  States.     By  Lkvi  W,  Leonaud." 

In  conformity  to  the  Act  of  the  Congress  of  the  United  States,  enti- 
tled, «  An  Act  for  the  encouragement  of  learning,  by  securing  the 
copies  of  maps,  charts,  and  books,  to  the  authors  and  proprietors 
of  such  copies,  during  the  times  therein  mentioned  ;"  and  also  to  an 
Act,  entitled,  "  An  Act,  supplementary  to  an  Act,  entitled,  An  Act 
for  the  encouragement  of  learning,  by  sjecuring  the  copies  of  maps, 
charts,  and  books,  to  the  authors  and  proprietors  of  such  copies,  dur- 
ing the  times  therein  mentioned ;  and  extending  the  benefits  thereof 
to  tho  arts  of  designing,  engravipg,  and  etching  historical,  and  other 
prints  " 

SAMUEL  CUSHMAN,   {  ^l}%tHLpsM:i:' 
A  true  Copy  of  Record : 

Attest  SAMUEL  CUSHMAN.  Clerk.. 


^- 


advertisement; 


The  following  Extracts  are  introduced  as  recommendatory 
of  the  design  of  the  Literary  and  Scientific  Class  Book. 

In  teaching  the  art  of  reading  it  is  an  obvious  waste  of  the 
precious  period,  devoted  to  education,  to  confine  the  exer- 
cises in  that  art  to  mere  combinations  of  words;  or  to 
compositions,  the  sole  object  of  which  is  to  prove  the  wit  and 
genius  of  the  writer  ;— to  compositions  which  do  not  teach 
any  thing,  and  which,  after  a  volume  of  them  has  been  pe- 
rused and  re-perused  for  years>  leave  the  mind  in  a  state  of 
listless  curiosity.  In  proof  of  the  justice  of  this  remark,  we 
need  only  appeal  to  the  feelings  of  those  persons,  who,  while 
they  were  at  school,  read  no  other  books  than  the  selections 
published  under  the  titles  of  Speakers,  Readers,  Extracts, 
and  Beauties.  As  exercises  in  elocution,  and  as  examples 
of  elegant  composition,  such  books  cannot  be  sufficientlj 
commended ;  but  they  are  ill  adapted  to  the  more  important 
objects  of  instruction,  and  with  regard  to  the  purposes  of 
general  knowledge,  they  bear  the  same  relation  that  gilding 
bears  to  gold,  or  pastime  to  useful  labour. Rev.  D.  Blair. 

It  is  evident  that  want  of  time  will  prevent  the  great  mass 
of  mankind  from  pursuing  a  systematic  course  of  education 
in  all  its  details ;  a  more  summary  and  compendious  method 
therefore  must  be  pursued  by  them.     The  great  majority 


JV  ADVERTISEMENT. 

must  be  content  with  never  going  beyond  a  certain  point, 
and  with  reaching  that  point  by  the  most  expeditious  route. 
A  few,  thus  initiated  in  the  truths  of  science,  will  no  doubt 
push  their  attainments  further ;  and  for  these  the  works  in 
common  use  will  suffice ;  but  for  the  multitude  it  will  be 
most  essential  that  works  should  be  prepared  adapted  to  their 

circumstances It  is   not  necessary  that  all  who  are 

taught  or  even  a  considerable  proportion  should  go  beyond 
the  rudiments  ;  but  whoever  feels  within  himself  a  desire  and 
an  aptitude  to  go  further  will  do  so, — and  the  chances  of  dis- 
covery, both  in  the  arts  and  in  science  itself,  will  be  thus 
indefinitely  multiplied.  Edinburgh  Review,  No.  81. 


PREFACE. 


The  Literary  and  Scientific  Class  Book,  by  the  Rev.  John 
Platts  of  Doncaster,  England,  was  published  in  the  begin- 
ning of  the  year  182L  "The  grand  object  aimed  at,"  he 
says  in  his  Preface,  "  is,  that  while  the  pupil  reads  his  daily 
lesson,  he  shall  not  only  learn  to  pronounce  words,  but  shall 
also  treasure  up  a  valuable  stock  of  ideas,  to  enlarge  his 
mind,  to  interest  his  heart,  and  to  prepare  him  for  his  future 
scenes  on  the  theatre  of  life." 

The  plan  and  leading  title  of  the  above-mentioned  publi- 
cation have  been  adopted  in  the  present  work,  and  many  of 
the  lessons  have  been  retained  either  in  full,  or  in  an  abridged 
and  altered  form.  The  notes,  appendix,  and  engravings, 
have  been  added ;  and  such  materials  have  been  selected 
from  other  sources  as  were  judged  best  adapted  to  improve 
the  hearts  and  enlarge  the  minds  of  youth  in  this  country. 
Most  of  the  lessons  have  been  selected  with  a  particular 
reference  to  the  instructio?i  which  they  contain  on  important 
branches  of  knowledge.  Although  the  work  is  designed 
for  the  higher  classes,  yet  it  is  believed  that  all  young  per- 
sons, who  are  able  to  read  with  facility,  and  are  acquainted 
with  the  rudiments  of  arithmetic  and  geography,  may  use  it 
with  advantage. 

The  names  of  authors  are  given  in  many  instances,  but,  in 
general,  the  quotations  have  been  so  much  altered,  or  the 
same  lesson  taken  from  so  many  different  sources,  that  it 
could  not  be  done  with  convenience.  The  works  consulted 
or  from  which  extracts  have  been  made,  are  noticed  in  the 
Appendix.  A  list  of  select  books  has  been  furnished  for  th« 
use  of  those  who  wish  to  make  further  attainments. 


SELECT  BOOKS. 

Locke's  Conduct  of  the  Understanding,  1  vol.  18mo. 

Watts'  Improvement  of  the  Mind,  12mo. 

Rett's  Elements  of  General  Knowledge,  2  vols.  12ino. 

Bezout's  Elements  of  Arithmetic,  12mo. 

Legendre's  Elements  of  Geometry,  8vo. 

Colburn's  Introduction  to  Algebra  upon  the  inductive  me* 
thod  of  Instruction,  1  vol.  12mo. 

Joyce's  Familiar  Introduction  to  the  Arts  and  Sciences,  1 
vol.  12  mo. 

Systematic  Education,  or  Elementary  Instruction  in  the 
various  departments  of  Literature  and  Science,  by  Rev. 
W.  Shepherd,  Rev.  J.  Joyce,  and  Rev.  L.  Carpenter,  2 
vols.  8vo. 

Cavallo's  Elements  of  Natural  and  Experimental  Philosophy^ 
by  F.  X.  Brosius,  2  vols.  8vo. 

Nicholson's  Operative  Mechanic     8vo. 

Nicholson's  Popular  Elements  of  pure  and  mixed  Mathe- 
matics, 8vo. 

Button's  Recreations  in  Mathematics  and  Natural  Philoso- 
phy, 4  vols.  8vo. 

Enfield's  Institutes  of  Natural  Philosophy,  Theoretical  and 
Practical,  4to. 

Ferguson's  Lectures  on  select  subjects  in  Mechanics,  Optics, 
Astronomy,  &c.  edited  by  Dr.  Brewster,  2  vols.  8vo. 

Ferguson's  Astronomy,  2  vols.  8vo.  edited  by  Dr.  Brewster. 

Bonny  castle's  Introduction  to  Astronomy,  1  vol.  8vo. 

Cotting's  Introduction  to  Chemistry,  12mo. 

Henry's  Elements  of  Chemistry,  2  vols.  8vo. 

Macneven's  Tabular  View  of  the  Modern  Nomenclature  and 
System  of  Chemistry. 

Mackenzie's  One  Thousand  Experiments  in  Chemistry,  ex- 
hibiting the  applications  of  Modern  Chemistry  to  all 
branches  of  the  useful  arts,  8vo. 

Cleveland's  Mineralogy  and  Geology,  2  vols.  8vo. 

Lowry's  Conversations  on  Mineralogy. 


Vm  SELECT  BOOKS. 

Robinson's  Catalogue  of  American  Minerals,  8vo. 

Locke's  Outlines  of  Botany,  12mo. 

Thornton's  Elements  of  Botany,  with  160  plates. 

Eaton's  Manual  of  Botany  for  the   Northern  and  Middle 

States,  12mo. 
Eaton's   Botanical    Exercises,   including    directions,  rules, 

&c.  12mo. 
Davy's  Agricultural  Chen>istry,  12mo. 

Brown's  Compendium  of  Agriculture,  12mo.  / 

Dean's  New  England  Farmer,  or  Georgical  Dictionary,  8vo(^ 
Willich's  Domestic  Encyclopsedia,  edited  by  Dn  Cooper,  S 

vols.  8vo. 
Benjamin's  Rudiments  of  Architecture,  8vo. 
Cabinet  Maker's  Guide. 
Gregory's  Economy  of  Nature,  3  vols.  8vo. 
Buffon's  Natural  History,  2  vols.  8vo. 
Paley's  Natural  Theology,  12nio, 
Harris'  Natural  History  of  the  Bible,  8vo. 
Harlan's  Description  of  the  Mammiferous  Animals  of  North 

America,  8vo. 
Bewick's  Quadrupeds,  1  vol.  8ro. 

Kirby  and  Spence's  Introduction  to  Entomology,  2  vols.  8vo. 
Worcester's  Sketches  of  the  Earth  and  its  inhabitants,  2  vols. 

12mo. 
Malte-Brun's  Universal  Geography,    or    description   of  all 

parts  of  the  world  on  a  new  Plan,  7  vols.  8vo. 
Bingley's  Useful  Knowledge,  3  vols.  12mo. 
Bigland's  Letters  on  the  Study  of  History,  8vo. 
Tytler's  Elements  of  History,  Ancient  and  Modern,  12mo. 
History  of  New  England  by  Hannah  Adams,  8vo. 
History  of  England,  abridged  from  Hume  and  Smollet,  by  J. 

Robinson,  D.  D. 
Paley's  Moral  and  Political  Philosophy,  8vo. 
Baker's  Moral  Philosophy,  abridged  from  Paley,  18mo. 
Parkhurst's  Elements  of  Moral  Philosophy,  12mo. 
Smith's  Wealth  of  Nations,  2  vols.  8vo. 
The  Federalist,  by  Madison,  Jay,  and  Hamilton,  Svo, 
Say's  Treatise  on  Political  Economy,  8vo. 
The  American  Journal  of  Science  and  Arts.     New-Haven. 
The  Boston  Journal  of  Philosophy  and  the  Arts. 
New  Edinburgh  Encyclopaedia,  edited  by  Dr.  Brewster. 


CONTENTS. 


LeEBon.  F&ge* 

1.  Intellectual  Pleasures,  -  -  1 

2.  Mental  Improvement,       -  -  •  -         3 

3.  Habit  of  Attentive  Thought,  .  -  5 

4.  Cultivation  of  Memory,     -  -  -  -         G 

5.  Plan  of  Reading,        -         -  -  -  8 

6.  Hymn  to  Science,  -  -  -  -       10 

7.  Usefulness  of  Mathematical  Studies,  -  13 

8.  Imagination, — its  Power  illustrated,        -  -       14 

9.  Beauty  and  Sublimity,  Illustration  of,  -  16 

10.  Taste,  Improvement  and  Pleasures  of,  -  -        IS 

11.  Poetry,— its  Object,         ....  20 

12.  Advantages  of  Studying  History,  -  -        21 

13.  Philosophy, — its  leading  Offices,     -  -  23 

14.  The  Praise  of  Philosophy,       -  -  -        25 

15.  General  Properties  of  Bodies,         -  -  -       27 

16.  Attraction  of  Gravitation.    Sir  Isaac  Newton's  Dis- 

coveries, r  -  -  -       .    -  30 

17.  Centre  of  Gravitv.     Pyramids  of  Egypt.     Tower 

of  Pisa,  ' 33 

18.  The  Laws  of  Motion.     Velocity,  Momenta,  Action 

and  Re-action,         -  -  _  -         _  35 

19.  Compound  Motion.     The  Pendulum,       -         -         37 

20.  Mechanical  Powers.     The  Lever,       -  -  -  40^ 

21.  The  Pulley,  Wheel,  and  Axle,  and  Inclined  Plane,  42 

22.  The  Wedge  and  Screw.     Friction,  -  -         44 

23.  The  Laws  of  Fluids.     Pressure  of  Fluids,    -  -  47 

24.  Specific  Gravity  of  Bodies.     Archimedes,         -         50 

25.  Hydraulics.     Syphon.    Common  Pump.     Forcing 

Pump,  -  ,  ,  -  -  -  52 

26.  The  Diving  Bell,  and  Steam  Engine,       -         -         54 

27.  Nature  and  Properties  of  Air.     The  Air  Pump,        56 

28.  The  Barometer,  Uses  of,  -  -  -  -  59 

29.  Sound.    Velocity  of  Sound.     Echo,         -         -         61 

30.  Nature  of  Musical  Sounds.     Musical  Barometer,      64 

31.  Optics.     Reflection  and  Refraction  of  Light,         -  66; 


M'^89^yl 


CONtENTS. 


33. 
34. 
35. 
36. 


41. 
42. 
43. 
44. 


Lesson.  Page. 

32.  Different  Kinds  of  Lenses.  Burning  Glass,  -  69 
Mirrors.     Convex  Reflectors,     -  -       -  -  71 

Colours.     The  Prism.  -  "         "         "         P 

The  Rainbow,  Halo,  and  Parhelia,      -         -         -    75 
Structure  of  the  Eye.     Angle  of  Vision,  -         78 

37.  Optical  Instruments.     Spectacles.     Microscopes,      81 

38.  Microscopic  Discoveries,  -  -  *         -    83 

39.  The  Telescope  and  Telegraph,       -         ^         -         86 

40.  Astronomy.  Progress  of  this  Science,  -  -  88 
The  Solar  System.  Galileo,  -  _  -  91 
The  Sun,  a  magnificent  habitable  globe,  -  -  93 
Mercury  and  Venus,  -  -  -  -  95 
The  Earth,  Ecliptic  and  Zodiac.  Celestial  Lati- 
tude and  Longitude,       -            -          -          -         97 

45.  Day  and  Night,  causes  of,         -  -         -         -  100 

46.  Changes  of  the  Seasons,       -  -  -  -       102 

47.  The  Moon.    Harvest  Moon,     -  -  -         -  104 

48.  The  Tides,  explanation  of,  -  -  -       107 

49.  Eclipses  of  the  Moon  and  Sun,  _  -         -  108 

50.  Mars,  Vesta,  Juno,  Pallas,  and  Ceres,     -  *       111 

51.  Jupiter, — his  Belts,  Satellites,  &c.      -  -         -  113 

52.  Saturn,  and  Uranus.  Saturn's  Ring,  -  -  114 
Comets.  Pope  Callixtus,  -  -  -  115 
The  Fixed  Stars.  The  Milky  Way,  -  -  117 
The  Constellations.  Hymn  to  the  North  Star,  119 
Forms  and  Divisions  of  Time.    Equation  of  Time,  122 

57.  The  Planetary  System,  -         -         -         -         125 

58.  Chemistry,  Importance  and  Use  of,  -         -    127 

59.  General  Principles  of  Chemistry.     Chemical  Af- 
finity, -..--.         128 

C-aloric.    Thermometer,             -         -         -        -    130 
Atmospheric  Air,  Composition  of  Oxygen.  Nitro- 
gen,      - 133 

Water,  Composition  of     Hydrogen  Gas,     -        -    135 
The  Earths  and  Alkalies.     Uses  of  Lime,  -     137 

Acids  and  Salts.     Mountains  of  Salt,     ^         -         140 
Simple  Combustibles.     Carbon.     Metals,  -      143 

66.  Oxyds  and  Combustion.     Exhilarating  Gas,        -    145 

67.  Electricity.     Electrical  Machine.    Experiments,     148 

68.  Leyden  Phial.  Dr.  Franklin's  Discovery.     Thun- 

der and  Lightning,  -  -  -        152 


53. 
54. 
55. 

56. 


60. 
61. 

62. 
63. 
64. 
65. 


CONTENTS.  XI 

Lesson.  Page. 

69.  Falling  Stars,  Water  Spouts,  and  Northern  Lights,  154 

70.  Galvanism.     Voltaic  Battery,         -  -  -  157 

71.  Galvanism  (continued.)     Prof.   Hare's  New  De- 

flagrator,  -  _  .  .,         159 

72.  Magnetism.     Variation  of  the  Needle,       -         •»     162 

73.  Magnetical  Experiments.     Amusing  Deceptions,    164 

74.  Aerostation.     Air  Balloons.     Parachute.     Death 

ofRozier,  _  _  _  -  166 

75.  Natural  History, — its  Objects,       -  -  -  169 

76.  Mineralogy.     Characters  of  Minerals,         -         -  172 

77.  Classification  of  Minerals.     The  Diamond,     -  174 

78.  Gold, — its  remarkable  ductility,  .         ^         -  176 

79.  Silver  and  Mercury.    Plating  with  Silver.    Quick- 

silver Mine,         -  -  -  -         _    178 

80.  Copper  and  Lead.     Brass.     White  Lead,       -         180 

81.  Iron  and  Tin.    Importance  of  Iron.     Use  of  Tin. 

Pewter,  -  -  -  -  -    182 

82.  Zinc,  Manganese,  and  Antimony,  their  Uses,  183 

83.  Study  of  Geology, — its  objects  and  uses,  -         185 

84.  Geology.  Stratification.  Sacred  History  confirmed,  186 

85.  Relative  Situation  of  Rocks.     Decomposition  of 

Rocks,         -  -  -  ^  -       189 

86.  Biographical  Sketch  of  Linna}us,     -  -         -    191 

87.  Study  of  Botany,  a  Source  of  Mental  Improve- 

ment,        -  .  -  _  -         194 

SS.  Texture  of  Vegetables.  Bark.    Wood.    Pith.    Age 

of  Trees,         -  -  -  -  -    196 

89.  Sap  and  Secretions,     Flowing  of  the  Sap.  Sugar,  198 

90.  Process  of  Vegetation,  -  -  -         200 

91.  Roots,  Stems,  Buds,  and  Leaves.     Effect  of  Light 

upon  Plants,  ^  .  -  .  202 

92.  Flower  and  Fruit,      ,  -  -  -         205 

93.  Classification  of  Vegetables,its  Importance  and  Use,  207 

94.  Flowers.     Insects  in  Flowers,  -  -         210 

95.  Animal  Kingdom.      Study  of  Zoology  advanta-r 

geous  to  the  Young,         -         ?  •?         -  212 

96.  First  Class  of  Animals  (Mammalia,)  Orders  of,  213 

97.  Birds,— their  Division  into  Orders.     Moulting,  217 

98.  Reptiles  and  Fishes.     Electrical  Fishes,         -  219 

99.  Structure  and  Transformation  of  Insects,       -  221 
100.  Orders  of  Insects.     The  Gossamer,        -            -  225 


Xli  CONTENTS. 

Lesson. 

101.  Crustaceous  and  Molluscous  Animals.     Shells, 

102.  Vermes  and  Zoophytes.     Leech.     Polypes,        -  230 

103.  Existence  of  the  Deity,         -         -         .        -  232 

104.  Political  Economy.     Progress  of  Civilization,      -  233 

105.  Property,  unequal  Distribution  of,  -         -  235 

106.  Division  of  Labour 237 

107.  Agriculture, — the  Strength  of  Nations,  -  239 

108.  Commerce  and  Manufactures,  -  -         _  240 

109.  Money, — its  abundance,  not  the  cause,  but  the  con- 

sequence of  Wealth,        -        -  -         -         242 

110  Ship-building  and  Navigation,     -        -        -         -    244 

111.  Architecture,  Advantages  of, — Orders  of,  -       246 

112.  Constitution  of  the  United  States,  Sketch  of,       -    248 

113.  Excellence  of  our  Republican  Government,      -       251 

114.  Intelligence  of  the  People  a  Means  of  Safety   to 

the  Government,     -  -  -  -         252 

115.  The  government  of  England.    King.  Parliament,  254 

116.  America  :  an  Extract  from  Bryant's  Poem  of  the 

Ages,  -----   257 

117.  Structure  of  the  Human  Body,            -             -  258 

118.  Structure  of  the  Human  Body,  (continued,)  -    260 

1 19.  The  Human  Voice,  wonderful  Mechanism  of,  262 

120.  Structure  of  the  Ear,          -         -             -  -    263 

121.  Music,  Pleasures  of,— Ear  for,             -             -  265 

122.  Painting.     Cartoons  of  Raphael,     -            -  -    267 

123.  Sculpture.  Statuary.  Casting  in  Plaster  of  Paris,  270 

124.  The  Love  of  Nature,         -             -             -  -    271 

125.  The  Importance  of  Natural  Philosophy,          -  272 

126.  Mythology,         -            -            -             -  -    274 

127.  Account  of  the  Principal  Heathen  Gods,         -  275 

128.  Account  of  the  Principal  Heathen  Goddesses,  -    278 

129.  Harmony  of  Science  and  Christianity,             -  280 

130.  The  Influence  of  an  Early  Taste  for  Reading,  281 

131.  The  Mechanical  Wonders  of  a  Feather,     -  -    282 

132.  Art  of  Making  Pins,         -             -        -          .  284 

133.  Clouds  and  Rain,      -            -          -          -  -    285 

134.  Invention  and  Progress  of  Printing,     '           -  287 

135.  Hope,  Influence  of,          -            ^             •  -    288 


THE 

LITERARY  AND  SCIENTIFIC 

CLASS  BOOK. 


LESSON  1. 

Intellectual  Pleasures^         ^■ 

Evolv'ed,  unfolded,  unrolled,  thrown  out, 
Transcen'dent,  excellent,  surpassing  others. 

WHEN  we  think  of  what  man  is,  not  in  his  faculties  only, 
but  in  his  intellectual  acquisitions,  and  of  what  he  must  have 
been,  on  his  entrance  into  the  world,  it  is  difficult  for  us  to 
regard  this  knowledge  and  absolute  ignorance  as  states  of 
the  same  mind.  It  seems  to  us  almost  as  if  we  had  to  con- 
sider a  spiritual  creation  or  transformation,  as  wondrous  a/s 
if,  in  contemplating  the  material  universe,  we  were  to  strive 
to  think  of  the  whole  system  of  suns  and  planets,  as  evolved 
from  a  mere  particle  of  matter,  or  rising  from  nothing,  as 
when  originally  created.  We  believe  that  they  were  so  cre- 
ated, and  we  know  that  man,  comprehensive  as  his  acquire- 
ments are,  must  have  set  out  in  his  intellectual  career  from 
absolute  ignorance ;  but  how  difficult  is  it  for  us  to  form  any, 
accurate  conception  of  what  we  thus  undoubtingly  believe  I 
The  mind,  which  is  enriched  with  as  many  sciences  as  there 
are  classes  of  existing  things  in  the  universe,  which  our  or- 
gans are  able  to  discern — the  mind,  which  is  skilled  in  all 
the  languages  of  all  the  civilized  nations  of  the  globe,  and 
which  has  fixed  and  treasured  in  its  own  remembrance,  the 
beauties  of  every  work  of  transcendent  genius,  which  age 
after  age  has  added  to  the  stores  of  antiquity — this  mind,  we 
know  well,  was  once  as  ignorant  as  the  dullest  and  feeblest 
of  those  minds,  which  scarcely  know  enough,  even  to  won- 
der at  its  superiority. 

That  pleasure  attends  the  sublime  operations  of  intellect 
ia  the  discovery  of  truth,  or  the  splendid  creations  of  fancy, 


<l  INTELLECTUAL   PLEASURES. 

or  the  various  arts  to  which  science  and  imagination  are 
subservient,  every  one  will  readily  admit,  to  whom  these 
operations  are  familiar.  But  the  great  masters  in  science 
and  art  are  few,  and  the  pleasure  which  they  feel  in  their 
noblest  inventions,  therefore,  would  be  but  a  slight  element 
in  the  sum  of  human  happiness.  The  joy,  however,  is  not 
confined  to  those,  who  have  the  pride  of  contemplating  these 
great  results  as  their  oivn.  It  exists  to  all  who  have  the 
humbler  capacity  of  contemplating  them  merely  as  results 
of  human  genius.  It  is  delightful  to  ham,  though  another 
may  have  been  the  discoverer ;  and  perhaps  the  pleasure 
which  a  mind  truly  ardent  for  knowledge,  feels  in  those  early 
years,  in  which  the  new  world  of  science  is  opened,  as  it 
were  to  its  view,  and  every  step,  and  almost  every  glance 
affords  some  new  accession  of  admiration  and  power,  may 
not  be  surpassed  even  by  the  pleasure  which  it  is  afterwards 
to  feel,  when  it  is  not  to  be  the  receiver  of  the  wisdom  of 
others,  but  itself  the  enlightener  of  the  wise. — Brown. 

Call  now  to  mind  what  high,  capacious  powers 

Lie  folded  up  in  man ;  how  far  beyond 

The  praise  of  mortals,  may  the  eternal  growth 

Of  nature  to  perfection  half  divine, 

Expand  the  blooming  soul :  what  pity  then 

Should  sloth's  unkindly  fogs  depress  to  earth 

Her  tender  blossom ;  choke  the  streams  of  life. 

And  blast  her  spring !  far  otherwise  designed 

Almighty  wisdom ;  nature's  happy  cares 

The  obedient  heart  far  otherwise  incline. 

Witness  the  sprightly  joy  when  aught  unknown 

Strikes  the  quick  sense,  and  wakes  each  active  power 

To  brisker  measures  ;  witness  the  neglect 

Of  all  familiar  objects,  though  beheld 

With  transport  once  ;  the  fond  attentive  gaze 

Of  young  astonishment ;  the  sober  zeal 

Of  age,  commenting  on  prodigious  things. 

For  such  the  bounteous  providence  of  heaven, 

In  every  breast  implanting  this  desire 

Of  objects  new  and  strange,  to  urge  us  on 

With  unremitted  labour  to  pursue 

Those  sacred  stores  that  wait  the  ripening  soul. 

In  truth's  exhaustless  bosom,  Akensios. 


MENTAL   IMPROVEMENT.  8 

LESSON  2. 

Mental  Improvement. 

Par'aphrase,  to  explain  in  many  words. 
Di'agram,  delineation  of  a  geometrical  figure. 

No  man  is  obliged  to  learri  and  know  every  thing,  for  it  is 
utterly  impossible ;  yet  all  persons  are  under  some  obliga- 
tion to  improve  their  own  understanding;  Universal  igno- 
rance or  infinite  errors  will  overspread  the  mind  which  is 
neglected,  and  lies  without  cultivation.  Skill  in  the  sciences 
is  indeed  the  business  and  profession  but  of  a  small  part  of 
mankind  •  but  there  are  many  others  placed  in  such  a  rank 
in  the  world,  as  allows  them  much  leisure  and  large  oppor- 
tunities to  cultivate  their  reason,  and  einrich  their  minds  with 
various  knowledge. 

The  common  duties  and  benefits  of  society,  which  belong 
to  every  man  living,  and  even  our  necessary  relations  to  a 
family,  a  neighbourhood,  or  government,  oblige  all  persons 
whatsoever  to  use  their  reasoning  powers  upon  a  thousand 
occasions ;  every  hour  of  life  calls  for  some  regular  exercise 
of  our  judgment  as  to  times  and  things,  persons  and  actions ; 
without  a  prudent  and  discreet  determination  in  matters  be- 
fore us,  we  shall  be  plunged  into  perpetual  errors  in  our  con- 
duct. Now  that  which  should  alv/ays  be  practised,  must  at 
some  time  be  learned. 

Besides,  every  son  and  daughter  of  Adam  has  a  most  im- 
portant concern  in  the  affairs  of  a  life  to  come,  and  therefore 
it  is  a  matter  of  the  highest  moment  for  every  one  to  under- 
stand, to  judge,  and  to  reason  right  about  the  things  of  re* 
ligion.  It  is  vain  for  any  to  say,  we  have  no  leisure  or  time 
for  it.  The  daily  intervals  of  time,  and  vacancies  from  ne- 
cessary labour,  together  with  the  one  day  in  seven  in  the 
Christian  world,  allow  sufficient  opportunity  for  this,  if  men 
would  but  apply  themselves  to  it  with  half  so  much  zeal  and 
diligence  as  they  do  to  the  trifles  and  amusements  of  this 
life  ;  and  it  would  turn  to  infinitely  better  account. 

There  are  five  eminent  means  or  methods  whereby  the 
mind  is  improved  in  the  knowledge  of  things  ;  and  these  are 
observation,  reading,  instruction  by  lectures,  conversation, 
and  meditation,  which  last,  in  a  peculiar  manner,  is  called 
Btudy. 


4  MENTAL    IMPROVEMENT. 

Observation  is  the  notice  that  we  take  of  all  occurrence^ 
in  human  life,  whether  they  are  sensible  or  intellectual 
whether  relating  to  persons  or  things,  to  ourselves  or  others 
It  is  this  that  furnishes  us,  even  from  our  infancy,  with  a  ricl 
variety  of  ideas  and  propositions,  words  and  phrases.  Al 
those  things  which  we  see,  hear  or  feel,  which  we  perceivi 
by  sense  or  consciousness,  or  which  we  know  in  a  direct  man- 
ner, with  scarce  any  exercise  of  our  reflecting  faculties  on 
our  reasoning  powers,  may  be  included  under  the  general 
name  of  observation.  There  is  no  time  or  place,  no  trans- 
actions, occurrences,  or  engagements  in  life,  which  exclude 
us  from  this  method  of  improving  the  mind. 

Reading  is  that  means  of  knowledge,  whereby  we  ac| 
quaint  ourselves  with  the  affairs,  actions,  and  thoughts  of  the 
living  and  the  dead,  in  the  most  remote  nations,  and  mosi 
distant  ages.  By  reading,  we  learn  not  only  the  actions  anc 
sentiments  of  different  nations  and  ages,  but  transfer  to  our- 
selves the  knowledge  and  improvements  of  the  most  learned 
men,  the  wisest  and  best  of  mankind.  It  is  another  advan- 
tage of  reading,  that  we  may  review  what  we  have  read  ;  wc 
may  consult  the  page  again  and  again,  and  meditate  on  it  a1 
successive  periods  in  our  retired  hours.  Unless  a  readei 
has  an  uncommon  and  most  retentive  memory,  there  if 
scarcely  any  book  or  chapter  worth  reading  once  that  is  noj 
worthy  of  second  perusal.  :| 

Public  or  private  lectures  are  such  verbal  instructions  as 
are  given  by  a  teacher  while  the  learners  attend  in  silence. 
An  instructer,  when  he  paraphrases  and  explains  other  au- 
thors, can  mark  out  the  precise  point  of  difficulty  or  contrcjj 
versy,  and  unfold  it.  When  he  teaches  us  natural  philoso- 
phy, or  most  parts  of  mathematical  learning,  he  can  convey 
to  our  senses  those  notions,  with  which  he  would  furnish  our 
minds.  He  can  make  the  experiments  before  our  eyes.  He 
can  describe  figures  and  diagrams,  point  to  the  lines  and 
angles,  and  by  sensible  means  make  out  the  demonstration 
in  a  more  intelligible  manner. 

Conversation  is  that  method  of  improving  our  mindfi| 
wherein  by  mutual  discourse  and  inquiry  we  learn  the  sen- 
timents of  others,  as  well  as  communicate  our  own.  By 
friendly  conference,  not  only  the  doubts  which  arise  in  the 
mind  upon  any  subject  of  discourse  are  easily  proposed  and 
solved,  but  the  very  difficulties  we  meet  with  in  books  an4 


HABIT  OF  ATTENTIVE  THOUGHT.  Q) 

ill  our  private  studies  may  find  a  relief.  A  man  of  vast 
reading,  without  conversation,  is  like  a  miser,  who  lives  only 
to  himself 

Meditation  or  study  includes  all  those  exercises  of  the 
mind,  whereby  we  render  all  the  former  methods  useful,  for 
our  increase  in  true  knowledge  and  wisdom.  By  meditation 
we  fix  in  our  memory  whatsoever  we  learn,  and  form  our 
own  judgment  of  the  truth  or  falsehood,  the  strength  or 
weakness  of  what  others  speak  or  write.  Neither  our  own 
observation,  nor  reading  the  works  of  the  learned,  nor  at- 
tendance on  the  best  lectures  of  instruction,  nor  enjoying 
the  brightest  conversation,  can  ever  make  a  man  truly  know- 
ing and  wise,  without  the  labours  of  his  own  reason  in  sur- 
veying, examining,  and  judging,  concerning  all  subjects 
upon  the  best  evidence  he  can  acquire. — Watts. 

Questions. — 1.  What  will  be  the  state  of  the  mind  if  unculti 
vated  ?  2.  To  what  exercise  do  the  common  duties  of  society 
obUge  all  persons  ?  3.  What  is  the  most  important  subject  on  which 
every  one  should  reason  correctly  ?  4.  What  are  the  most  suitable 
opportunities  for  this  duty  ?  5.  What  are  the  five  eminent  means  of 
knowledge  ?  6.  What  is  observation  ?  7.  Reading  ?  8.  What  are 
lectures  ?  9.  What  is  included  in  meditation  or  study  ?  10.  What 
are  some  of  the  advantages  of  each  of  these  five  means  of  knowledge  ."• 


LESSON  3. 
Habit  of  Attentive  Thought. 

Griffin,  a  fabled  animal. 
Tal'isman,  a  magical  character. 

It  is  of  great  importance  to  your  intellectual  improvement 
that  you  should  acquire  the  habit  of  attentive  thought.  The 
primary  recommendation  of  science  is  its  utility ;  and  if  you 
are  really  desirous  of  advancing  in  it,  you  will  not  regard  the 
occasional  ruggedness  of  a  road,  which  is  far  from  beincr  «/- 
ways  rugged.  It  may  be  allowed  to  him,  who  walks  only 
for  the  pleasure  of  the  moment  to  turn  away  from  every  path, 
in  which  he  has  not  flowers  and  verdure  beneath  his  feet' 
and  beauty  wherever  he  looks  around.  But  in  that  know- 
ledge which  awaits  your  studies,  in  the  various  sciences  to 
which  your  attention  may  be  directed,  you  have  a  noble  prize 
before  you ;  and,  therefore,  you  should  not  hesitate  occa- 
1  * 


6  CULTIVATION    OP   MEMORY,  ] 

sionally  to  put  forth  all  the  vigour  of  your  attention,  at  thei 
risk  of  a  little  temporary  fatigue.  It  will  facilitate  your  ac*^ 
quisition  of  a  reward,  which  the  listless  exertions  of  the  iii'i 
dolent  can  never  obtain. 

It  is  in  science,  or  philosophy,  as  in  many  a  fairy  tale.  Thei 
different  obstacles  which  the  hero  encounters,  are  not  pro^i 
gressively  greater  and  greater  ;  but  his  most  difficult  achieve*^ 
ments  are  often  at  the  very  commencement  of  his  careers 
He  begins,  perhaps,  with  attacking  the  castle  of  some  en-^ 
chanter,  and  has  to  force  his  way,  unassisted,  through  thd 
griffins  and  dragons  that  oppose  his  entrance.  He  finishei^ 
the  adventure  with  the  death  of  the  magician — and  strips 
him  of  some  ring,  or  other  talisman,  which  renders  his  sutn 
sequent  adventures  comparatively  easy  and  secure.  The 
habit  of  attentive  thought,  which  the  consideration  of  diffi-^ 
cult  subjects  necessarily  produces,  in  those  who  are  not  toq 
indolent  to  give  attention  to  them,  or  too  indifferent  to  fee| 
interest  in  them,  is  more  truly  valuable  than  any  talisman,  of; 
which  accident  or  force  might  deprive  you.  The  magid 
with  which  this  endows  you,  is  not  attached  to  a  ring,  or  a 
gem,  or  any  thing  external ;  it  lives,  and  lives  for  ever,  in  th0 
very  essence  of  your  minds. — Brown.  i 

LESSON  4.  I 

\ 
Cultivation  of  Memory.  w 

■    Super'fluous,  unnecessary.  '), 

Cha'os,  confusion,     ch  in  words  from  the  Greek  sound  like  k. 

Memory  implies  two  things  :  first,  a  capacity  of  retaining 
knowledge ;  and,  secondly,  a  power  of  recalling  that  know- 
ledge  to  our  thoughts  when  we  have  occasion  to  apply  it  to 
use.  When  we  speak  of  a  retentive  memory,  we  use  it  il| 
the  former  sense ;  when  of  a  ready  memory,  in  the  latter^ 
Without  memory,  there  can  be  neither  knowledge,  arts,  noli 
sciences ;  nor  any  improvement  of  mankind  in  virtue,  oi^ 
morals,  or  the  practice  of  religion.  Without  memory,  th^ 
soul  of  man  would  be  but  a  poor,  destitute,  naked  being,  with 
an  everlasting  blank  spread  over  it,  ?^xcept  the  fleeting  ideaai 
of  the  present  moment.  | 


CULTIVATION    OP   MEMORY.  7 

There  is  one  great  and  general  direction,  which  belongs 
to  the  improvement  of  other  powers  as  well  as  of  the  me- 
mory, and  that  is,  to  keep  it  always  in  dne  and  proper  exer- 
cise. Many  acts  by  degrees  form  a  habit,  and  thereby  the 
capacity  or  power  is  strengthened  and  made  more  retentive 
and  ready.  Due  attention  and  diligence  to  learn  and  know 
the  things  which  we  would  commit  to  our  remembrance,  is 
a  rule  of  great  necessity.  There  are  some  persons,  who  com- 
plain they  cannot  remember  what  they  hear,  when  in  truth 
their  thoughts  are  wandering  half  the  time,  or  they  hear  with 
such  coldness  and  indifference,  and  a  trifling  temper  of  spi- 
rit, that  it  is  no  wonder  the  things  which  are  read  or  spoken 
make  but  a  slight  impression,  and  soon  vanish  and  are  lost. 
If  we  would  retain  a  long  remembrance  of  the  things  which 
we  read  or  hear,  we  should  engage  our  delight  and  pleasure 
in  those  subjects,  and  .use  proper  methods  to  fix  the  atten- 
tion. Sloth  and  idleness  will  no  more  bless  the  mind  with 
intellectual  riches,  than  they  will  fill  the  hand  with  gain,  the 
field  with  corn,  or  the  purse  with  treasure. 

Some  persons  are  conceited  of  their  abilities,  and  trust  so 
much  to  an  acuteness  of  parts  denominated  genius,  that  they 
think  it  superfluous  labour  to  make  any  provision  before- 
hand, and  they  sit  still,  therefore,  satisfied  without  endeavour- 
ing to  store  their  understanding  with  knowledge.  Such 
should  remember  that  we  are  born  ignorant  of  every  thing. 
God  has  made  the  intellectual  world  harmonious  and  beauti- 
ful without  us  ;  but  it  will  never  come  into  our  heads  all  at 
once  ;  we  must  bring  it  home  by  degrees,  and  there  set  it  up 
by  our  own  industry,  or  we  shall  have  nothing  but  darkness 
and  chaos  within,  whatever  order  and  light  there  may  be  in 
things  without  us. 

Others,  on  the  contrary,  depress  their  own  minds,  despond 
at  the  first  difficulty,  and  conclude  that  getting  an  insight  in 
any  of  the  sciences,  or  making  any  progress  in  knowledge, 
farther  than  serves  their  ordinary  business,  is  above  their  ca- 
pacities. The  proper  remedy  here  is  to  set  the  mind  to  work, 
and  apply  the  thoughts  vigorously  to  the  business  ;  for  it  holds 
in  the  struggles  of  the  mind,  as  in  those  of  war, — a  persua- 
sion that  we  shall  overcome  any  difficulties  that  we  may  meet 
with  in  the  sciences,  seldom  fails  to  carry  us  through  them. 
Nobody  knows  the  strength  of  his  mind,  and  the  force  of 
steady  and  regular  application,  until  he  has  tried. 


5  PLAN    OF    READING. 

All  things  are  open  to  the  searching  eye 
Of  an  attentive  intellect,  and  bring 
Their  several  treasures  to  it,  and  unfold 
Their  fabric  to  its  scrutiny.     All  life, 
And  all  inferior  orders,  in  the  waste 
Of  being  spread  before  us,  are  to  him. 
Who  lives  in  meditation,  and  the  search 
Of  wisdom  and  of  beauty,  open  books, 
Wherein  he  reads  .the  Godhead,  and  the  ways 
He  works  through  his  creation,  and  the  links 
That  fasten  us  to  all  things,  with  a  sense 
Of  fellowship  and  feeling,  so  that  we 
Look  not  upon  a  cloud,  or  falling  leaf. 
Or  flower  new  blown,  or  human  face  divine. 
But  we  have  caught  new  life,  and  wider  thrown 
The  door  of  reason  open,  and  have  stored 
In  memory's  secret  chamber,  for  dark  years 
Of  age  and  weariness,  the  food  of  thought. 
And  thus  extended  mind,  and  made  it  young, 
When  ihe  tnin  Imir  turns  gray,  and  feeling  dies. 

Percival. 

Questions. — 1.  What  does  memory  imply?  2.  What  general 
direction  is  given  for  the  improvement  of  memory  ?  3.  What  is  a 
rule  of  great  necessity  ?  4.  What  is  said  of  those  who  are  conceited 
of  their  abilities  ?  5.  What  is  the  proper  remedy  for  those  who  de- 
gpond  at  difficulties  ? 


LESSON  5. 

Plan  of  Reading.  ^ 

■A 

Specula'tion,  a  train  of  thoughts  formed  by  meditation.  1 

Discrimina'tion,  the  act  of  distinguishing  one  from  another.  | 

Desidera'ta,  pi.  some  desirable  things  which  are  wanted.  ■'- 
Lab'yrinth,  a  place  formed  with  inextricable  windings. 

The  only  method  of  putting  our  acquired  knowledge  on  a  i 
level  with  our  original  speculations,  is,  after  making  our-  ; 
selves  acquainted  with  our  author's  ideas,  to  study  the  sub-  5 
ject  over  again  in  our  own  way  ;  to  pause,  from  time  to  time,  \ 
in  the  course  of  our  reading,  in  order  to  consider  what  we  i 
taye  gained  ;  to  recollect  what  the  propositions  are,  which  ; 
the  author  wishes  to  establish,  and  to  examine  the  different  .i 


fLAN    OP   READING. 


# 


proofs  which  he  employs  to  support  them.  Such  reasonings, 
as  we  have  occasion  frequently  to  apply,  either  in  the  busi- 
ness of  life,  or  in  the  course  of  our  studies,  it  is  of  impor- 
tance to  us  to  commit  to  writing,  in  a  language  and  in  an 
order  of  our  own ;  and  if,  at  any  time,  we  find  it  necessary 
to  refresh  our  recollection  on  the  subject,  to  have  recourse 
to  our  own  composition,  in  preference  to  that  of  any  other 
author. 

That  the  plan  of  reading,  commonly  followed,  is  very  dif- 
ferent from  that  which  is  here  recommended,  will  not  be 
disputed.  Most  people  read  merely  to  pass  an  idle  hour,  or 
to  please  themselves  with  the  idea  of  employment,  while 
their  indolence  prevents  them  from  any  active  exertion  ;  and 
a  considerable  number  with  a  view  to  the  display  which  they 
are  afterwards  to  make  of  their  literary  acquisitions.  From 
whichsoever  of  these  motives  a  person  is  led  to  the  perusal 
of  books,  it  is  hardly  possible  that  he  can  derive  from  them 
any  material  advantage.  If  he  reads  merely  from  indolence, 
the  ideas  which  pass  through  his  mind  will  probably  leave 
little  or  no  impression ;  if  he  reads  from  vanity,  he  will  be 
more  anxious  to  select  striking  particulars  in  the  matter  or 
expression,  than  to  seize  the  spirit  and  scope  of  the  author's 
reasoning,  or  to  examine  how  far  he  has  made  any  additions 
to  the  stock  of  useful  and  solid  knowledge. 

A  proper  selection  of  the  particulars  to  be  remembered  is 
necessary  to  enable  us  to  profit  by  reading.  When  we  first 
enter  on  any  new  literary  pursuit,  we  commonly  find  our  ef- 
forts of  attention  painful  and  unsatisfactory.  We  have  no 
discrimination  in  our  curiosity,  and  by  grasping  at  every 
thing,  we  fail  in  making  those  moderate  acquisitions  which 
are  suited  to  our  limited  faculties.  As  our  knowledge  ex- 
tends, we  learn  to  know  what  particulars  are  likely  to  be  of 
use  to  us,  and  acquire  a  habit  of  directing  our  examinations 
to  these,  without  distracting  the  attention  with  others.  It 
is  partly  owing  to  a  similar  circumstance,  that  most  readers 
complain  of  a  defect  of  memory,  when  they  first  enter  on 
the  study  of  history.  They  cannot  separate  important  from 
trifling  facts,  and  they  find  themselves  unable  to  retain  any 
thing  from  their  anxiety  to  secure  the  whole. 

In  order  to  give  a  proper  direction  to  our  attention  to  the 
course  of  our  studies,  it  is  useful  before  engaging  in  any  par- 
ticular pursuits  to  acquire  as  familiar  an  acquaintance  as 


10  HYMN    TO    SCIENCE.  ^ 

possible  with  the  great  outlines  of  the  different  branches  off 
science ;  with  the  most  important  conclusions  which  hava^ 
hitherto  been  formed  in  them,  and  with  the  most  importanii 
desiderata  which  remain  to  be  supplied.  By  such  generaj 
views  alone  we  can  prevent  ourselves  from  being  lost  amidst 
a  labyrinth  of  particulars,  or  can  engage  in  a  course  of  exi« 
tensive  and  various  reading,  with  an  enlightened  and  di*«i 
criminating  attention. — Stewart.  i 

Questions. — 1.  By  what  method  may  our  acquired  knowledge  bd 
put  on  a  level  with  our  original  speculations  ?  2.  What  reasonings  vl^ 
it  important  to  commit  to  writing  ?  3.  What  plan  of  reading  is  comt 
monly  followed  ?  4.  What  are  its  disadvantages  ?  5.  Why  should  t^ 
proper  selection  be  made  of  the  objects  of  knowledge  ?  G.  What  i^ 
useful  before  engaging  in  any  particular  pursuits  ?  7.  What  will  aW 
acquaintance  with  the  great  outlines  of  science  prevent  ,'*  'i 


LESSON  6. 

Hy7nn  to  Science. 


Scho'liast,  a  writer  of  explanatory  notes.  ^'■ 

Soph'ist,  a  plausible  but  false  reasoner.  >1 

Science  !  thou  fair  effusive  ray  \ 

From  the  great  source  of  mental  day,  j 

Free,  gen'rous,  and  refined,  % 

Descend  with  all  thy  treasures  fraught,  ^,, 

Illumine  each  bewilder'd  thought,  i 

And  bless  my  lab'ring  mind. 

But  first  with  thy  resistless  light  ^ 

Disperse  those  phantoms  from  my  sight,  '^ 

Those  mimic  shades  of  thee,  ] 

The  scholiast's  learning,  sophist's  cant,  ^ 

The  visionary  bigot's  rant,  • 

The  monk's  philosophy.  ^ 

Oh  !  let  thy  powerful  charm  impart  -i 

The  patient  head,  the  candid  heart,  ^ 

Devoted  to  thy  sway  ;  l 

Which  no  weak  passions  e'er  mislead,  i 
Which  still  with  dauntless  steps  proceed 

Where  reason  points  the  way.  I 

I 


HYMN   TO    SCIENCE.  ]l 

Give  me  to  learn  each  secret  cause  j 
het  numbers,  figures,  motion's  laws, 

Reveal'd  before  me  stand ; 
Then  to  great  nature's  scenes  apply, 
And  round  the  globe  and  through  the  sky 

Disclose  her  working  hand. 

Next  to  thy  nobler  search  resign'd 
The  busy  restless  human  mind 

Through  ev'ry  maze  pursue  ; 
Detect  perception  where  it  lies, 
Catch  the  ideas  as  they  rise, 

And  all  their  changes  view. 

Her  secret  stores  bid  Mem'ry  tell, 
Bid  Fancy  quit  her  airy  cell 

In  all  her  treasures  drest ; 
While,  prompt  her  sallies  to  control, 
Reason,  the  judge,  recalls  the  soul 

To  truth's  severest  test. 

Say  from  what  simple  springs  began 
The  vast  ambitious  thoughts  of  man, 

That  range  beyond  control. 
Which  seek  eternity  to  trace, 
Drive  through  the  infinity  of  space, 

And  strain  to  grasp  the  whole  ? 

Then  range  through  being's  wide  extent, 
Let  the  fair  scale  with  just  ascent 

And  equal  steps  be  trod, 
Till,  from  the  dead  corporeal  mass, 
Through  each  progressive  rank  you  pass 

To  instinct,  reason,  God  ! 

There,  Science,  veil  thy  daring  eye, 
Nor  dive  too  deep,  nor  soar  too  high, 

In  the  divine  abyss  ; 
To  faith  content  thy  beams  to  lend. 
Her  hopes  t'  assure,  her  steps  befriend, 

And  light  the  way  to  bliss. 

Then  downward  take  thy  flight  again, 
Mix  with  the  policies  of  men. 
And  social  Nature's  ties 


12  ifYMN    TO    SCIENCE. 

The  plan,  the  genius,  of  each  state,  j 

Its  interest  and  its  power  relate,  ' 
Its  fortunes  and  its  rise. 

Through  private  life  pursue  thy  course  , 

Trace  ev'ry  action  to  its  source,  { 

And  means  and  motives  weigh ;  a 

Put  tempers,  passions,  in  the  scale,  i 

Mark  what  degrees  in  each  prevail,  J 

And  fix  the  doubtful  sway.  j 

The  last,  best  effort  of  thy  skill,  [ 

To  form  the  life,  and  rule  the  will,  I 

Propitious  Pow'r  !  impart ;  -^ 

Teach  me  to  cool  my  passions'  fires,  { 

Make  me  the  judge  of  my  desires,  ] 

The  master  of  my  heart.  ''■■ 

Raise  me  above  the  vulgar  breath,  i 

Pursuit  of  fortune,  dread  of  death  'i 

And  all  in  life  that's  mean :  i 

Still  true  to  reason  be  my  plan,  i 

And  let  my  actions  speak  the  man,  ^i 

Through  ev'ry  varying  scene.  i 

Hail,  queen  of  manners!  test  of  truth!  ' 
Hail,  charm  of  age,  and  light  of  youth  I 

Sweet  refuge  of  distress  !  | 

E'en  business  you  can  make  polite,  J 

Can  give  retirement  its  delight,  ] 

Prosperity  its  grace. 

Of  pow'r,  wealth,  freedom,  thou  the  cause,  i 

Foundress  of  order,  cities,  laws,  i 

Of  arts  inventress  thou  !  j 

Without  thee,  what  were  human  kind  !  l 
How  vast  their  wants,  their  thoughts  how  blind !         ^ 

Their  joys  how  mean,  how  few !  i 

Sun  of  the  soul !  thy  beams  unveil !  j 
Let  others  spread  the  daring  sail 

On  fortune's  faithless  sea :  j 

While  undeluded,  happier  I  j 
From  the  vain  tumult  timely  fly, 

And  sit  in  peace  with  thee.  \ 


MATHEMATICAL   STUPIES.  13 


LESSON  7. 


Usefulness  of  Mathematical  Studies. 

Ax'ioms,  maxims,  self-evident  propositions. 
Anal'ogy,  resemblance — see  Hedge's  or  Jamieson's  Logic. 
Phys'ics,  natural  philosophy,  or  the  doctrine  of  natural  bodies, 
their  various  appearances,  affections,  motions,  operations,  &c. 

Of  all  the  sciences  which  serve  to  call  forth  the  spirit  of 
enterprise  and  inquiry,  there  is  none  more  eminently  useful 
than  mathematics.  By  an  early  attachment  to  these  elegant 
and  sublime  studies  we  acquire  a  habit  of  reasoning,  and  an 
elevation  of  thought,  which  fixes  the  mind,  and  prepares  it 
for  every  other  pursuit.  From  a  few  simple  axioms,  and 
evident  principles,  we  proceed  gradually  to  the  most  general 
propositions,  and  remote  analogies  :  deducing  one  truth  from 
another  in  a  chain  of  argument  well  connected  and  logically 
pursued ;  which  brings  us  at  last,  in  the  most  satisfactory 
manner,  to  the  conclusion,  and  serves  as  a  general  direction 
in  all  our  inquiries  after  truth. 

Mathematical  learning  is  likewise  equally  estimable  for  its 
practical  utility.  Almost  all  the  works  of  art  and  devices  of 
man,  have  a  dependence  upon  its  principles,  and  are  indebt- 
ed to  it  for  their  origin  and  perfection.  The  cultivation  of 
these  admirable  sciences  is  therefore  a  thing  of  the  utmost 
importance,  and  ought  to  be  considered  as  a  principal  part 
of  every  well  regulated  plan  of  education.  They  are  the 
guide  of  our  youth,  the  perfection  of  our  reason,  and  the 
foundation  of  every  great  and  noble  undertaking. 

Mathematics  are  very  properly  recommended  as  the  best 
remedy  to  cure  an  unsteady  and  volatile  disposition.  They 
teach  us  to  reason  in  a  clear  and  methodical  manner.  They 
give  a  manly  vigour  to  our  understanding,  and  free  us  from 
doubt  and  uncertainty  on  the  one  hand,  and  credulity  and 
rash  presumption  on  the  other.  These  studies  are  calcu- 
lated to  teach  exactness  and  perspicuity  in  definition,  con- 
nexion and  conclusiveness  in  argument,  carefulness  in  ob- 
servation, patience  in  meditation  ;  and  from  no  exercises  can 
ihe  scholar  go  better  prepared  and  disciplined  to  the  pursuit 
of  the  higher  branches  of  knowledge.  The  benefit  to  be 
derived  from  them  is  thus  stated  by  Mr.  Locke :  "  I  have 
mentioned  mathematics  as  a  way  to  settle  in  the  mind  a 
2 


14  IMAGINATION. 

habit  of  reasoning  closely,  ^nd  in  train ;  not  that  I  think  i 
necessary  that  all  men  should  be  deep  mathematicians ;  bu 
that  having  got  the  way  of  reasoning,  to  which  that  stud 
necessarily  brings  the  mind,  they  might  be  able  to  transfe 
it  to  other  parts  of  knowledge,  as  they  shdl  have  occasion; 
Mathematics,  according  to  their  proper  definition,  const 
tute  the  science  of  quantity,  either  as  subject  to  measure  c 
number.  They  are  pure  and  mixed.  The  former  conside 
Quantity  abstractedly,  without  any  regard  to  matter  or  pai 
ticular  bodies ;  the  latter  treat  of  quantity  as  subsisting  i 
bodies,  and  consequently  they  are  intermixed  with  the  coi 
sjderation  of  physics,  or  experimental  philosophy. 

Rett's  Elements  of  General  Knowledge.  ^ 

Questions. — 1.  Whnt  habit  does  an  early  attention  to  mathemi 
tical  studies  produce  ?  2.  What  is  said  of  their  practical  utility 
3.  What  are  they  calculated  to  teach  ?  4.  How  is  the  benefit  to  I 
derived  from  them  stated  by  Mr.  Locke  ?  5.  Give  a  definition  ( 
mathematics.  C.  Mow  do  pure  mathematics  consider  quantity  ? 
Mixed.? 

Note.  Pure  mathematics  are  arithmetic,  algebra,  geometry,  ar 
fluxions :  mixed  consist  chiefly  of  mochanics,  pneumatics,  hydn 
statics,  optics,  and  astronomy. 

^  i 

LESSON  8.  ^ 

Imagi7iation. 

We  do  not  merely  perceive  objects,  and  conceive  or  r* 
member  them  simply  as  they  were,  but  we  have  the  power  c 
combining  them  in  various  new  assemblages, — of  formin 
at  our  will,  with  a  sort  of  delegated  omnipotence,  noti 
single  universe  merely,  but  a  iieii^  and  varied  universe,  wit 
every  succession  of  our  thought.  The  materials  of  whic 
we  form  them  are,  indeed,  materials  that  exist  in  ever 
mind ;  but  they  exist  in  every  mind  only  as  the  stones  exii 
shapelessly  in  the  quarry,  that  require  little  more  than  m( 
chanic  labour  to  convert  them  into  cornmon  dwellings,  bi 
that  rise  into  palaces  and  temples  only  at  the  command  o 
architectural  genius.  This  power  of  combining  our  coi 
ceptions  or  remembrances  in  new  assemblages  is  terme 
imagination. 

The  most  sublime  exertions  of  imagination  are  made  b 


IMAGINATION.  15 

the  poet.  But  we  must  not  conceive,  merely  because  they 
are  sublime,  that  they  comprehend  the  whole  ojQice  of  ima* 
gination,  or  even  its  most  important  uses.  It  is  of  far  more 
importance  to  mankind,  as  it  operates  in  the  common  offices 
of  life, — in  the  familiar  feelings  of  every  hour.  What  are 
all  those  pictures  of  the  future,  which  are  ever  before  our 
eyes,  in  the  successive  hopes,  and  fears,  and  designs  of  life, 
but  imaginations,  in  which  circumstances  are  combined  that 
never  perhaps,  in  the  same  forms  and  proportions,  have  ex- 
isted in  reality,  and  which,  very  probably,  are  never  to  exist 
but  in  those  very  hopes  and  fears  which  we  have  formed  ? 
The  writer  of  romance  gives  secret  motions  and  passions  to 
the  characters  which  he  invents,  and  adds  incident  to  inci- 
dent in  the  long  series  of  complicated  action  which  he  de- 
velopes.  What  he  does,  we,  too,  are  doing  every  hour ; — ' 
contriving  events  that  never  are  to  happen, — imagining  mo- 
tives and  passions,  and  thinking  our  little  romances,  of  which 
ourselves,  perhaps,  are  the  primary  heroes,  but  in  the  plot 
of  which  there  is  a  sufficient  complication  of  adventures  of 
those  whom  we  love,  and  those  whom  we  dislike.  Our  ro- 
mances of  real  life,  though  founded  upon  facts,  are,  in  their 
principal  circumstances,  fictions  still  ;  and,  though  the  fancy 
which  they  display  may  not  be  as  brilliant,  it  is  still  the  same 
in  kind  with  that  which  forms  and  fills  the  history  of  imagi- 
nary heroes  and  heroines. 

It  is  well  known,  from  experience,  that  the  activity  and 
consequent  improvement  of  imagination,  depend  not  a  little 
upon  the  character  of  the  objects  with  which  it  is  first  occu- 
pied. The  great,  the  sublime,  the  beautiful,  the  new,  and 
the  uncommon,  in  external  nature,  are  not  only  striking  and 
agreeable  in  themselves,  but,  by  association,  these  qualities 
powerfully  awaken  the  sensibilities  of  the  heart,  and  kindle 
the  fires  of  youthful  imagination.  If  the  student  permit 
objects  which  are  mean,  low,  or  sensual,  to  usurp  possession 
of  his  mind ;  if  the  books  which  he  reads,  and  the  studies 
that  he  pursues,  are  contaminated  with  gross  ideas,  he  has 
no  right  to  expect  that  this  omnipotent  faculty  shall  ever 
draw  from  the  polluted  treasures  of  his  memory,  any  thing 
noble,  useful,  or  praiseworthy ;  or  that  his  name  shall  ever 
be  enrolled  among  those  who  have  delighted,  instructed,  and 
honoured  their  native  land  and  the  world  at  large. 

By  an  excessive  indulgence  in  the  pleasures  of  imagina- 


16  BEAUTY   AND    SUBLIMITY. 

tion,  the  taste  may  acquire  a  fastidious  refinement  unsuitable 
to  the  present  situation  of  human  nature ;  and  those  intel- 
lectual and  moral  habits,  which  ought  to  be  formed  by  ac- 
tual experience  of  the  world,  may  be  gradually  so  accommo- 
dated to  the  dreams  of  poetry  and  romance,  as  to  disqualify 
us  for  the  scenes  in  which  we  are  destined  to  act.  But  a 
well-regulated  imagination  is  the  great  spring  of  human  ac- 
tivity, and  tlie  principal  source  of  human  improvement.  As 
it  delights  in  presenting  to  the  mind  scenes  and  characters 
more  perfect  than  those  with  which  we  are  acquainted,  it 
prevents  us  from  ever  being  completely  satisfied  with  our 
present  condition,  or  with  our  past  attainments,  and  engages 
us  continually  in  the  pursuit  of  some  untried  enjoyment,  or 
of  some  ideal  excellence.  Destroy  this  faculty,  and  the  con- 
ditioft  of  man  will  become  as  stationary  as  that  of  the  brutes. 

Questions. — 1.  What  is  imagination  ?  2.  By  whom  are  its  most 
sublime  exertions  made  ?  3.  Illustrate  its  operation  in  the  common 
offices  of  life.  4.  On  what  do  the  activity  and  improvement  of  ima- 
gination greatly  depend  ?  5.  What  may  be  the  consequence  of  an 
excessive  indulgence  in  the  pleasures  of  imagination  .''  6.  Why  is  a 
well-regulated  imagination  the  great  spring  of  human  activity,  and 
source  of  human  improvement  ? 


LESSON  9. 

Beauty  and  Sublimity. 

Emo'tions,  vivid  feelings  arising  immediately  from  the  consider- 
ation of  objects,  perceived,  remembered,  or  imagined. 

Cartoon',  a  painting  or  drawing  upon  several  sheets  of  large  paper 
pasted  on  canvass.  The  most  celebrated  are  the  cartoons  of 
Raphael.     See  Lesson  on  Painting. 

Our  emotions  of  beauty  are  various  ;  and,  as  they  gra- 
dually rise,  from  object  to  object,  a  sort  of  regular  progres- 
sion may  be  traced  from  the  faintest  beauty  to  the  vastest 
sublimity.  These  extremes  may  be  considered  as  united, 
by  a  class  of  intermediate  feelings,  for  which  grandeur  might, 
perhaps,  be  a  suitable  term,  that  have  more  of  beauty,  or 
more  of  sublimity,  according  to  their  place  in  the  scale  of 
emotion.  Let  us  imagine  that  we  see  before  us  a  stream 
gently  gliding  through  fields,  rich  with  all  the  luxuriance  of 
summer,  overshadowed  at  times  by  the  foliage  that  hangs 


BEAUTY    AND    SUBLIMITY.  17 

over  it,  from  bank  to  bank,  and  then  suddenly  sparkling  in 
the  open  sunshine,  as  if  with  a  still  brighter  current  than 
before.  Let  us  trace  it,  till  it  widens  to  a  majestic  river,  of 
which  the  waters  are  tlie  boundary  of  two  flourishing  em- 
pires, conveying  abundance  equally  to  each,  while  city  suc- 
ceeds city,  on  its  populous  shores,  almost  with  the  same  ra- 
pidity as  grove  formerly  succeeded  grove.  Let  us  next  be- 
hold it  losing  itself  in  the  immensity  of  the  ocean,  which 
seems  to  be  only  an  expansion  of  itself,  when  there  is  not  an 
object  to  be  seen  but  its  own  wide  amplitude,  between  the 
banks  which  it  leaves,  and  the  sun  that  is  setting,  as  if  in 
another  world,  in  the  remote  horizon ; — in  all  this  course, 
from  the  brook  to  the  boundless  waste  of  waters, — if  we 
were  to  trace  and  contemplate  the  whole  continued  progress, 
we  should  have  a  series  of  emotions.  The  emotions  which 
rose,  when  we  regarded  the  fiarroio  stream,  would  be  those 
which  we  class  as  emotions  of  beaut?/.  The  emotions  which 
rose  when  we  considered  that  infinity  of  waters,  in  which  it 
was  ultimately  lost,  would  be  of  the  kind  which  we  deno- 
minate sublimit?/ ;  and  the  grandeur  of  the  river,  while  it 
was  still  distinguishable  from  the  ocean,  to  which  it  was  pro- 
ceeding, might  be  viewed  with  feelings,  to  which,  on  the 
same  principle  of  distinction,  some  other  name  or  names 
might  be  given. 

The  same  progressive  series  of  feelings,  which  may  thus 
be  traced  as  we  contemplate  works  of  nature,  is  not  less  evi- 
dent in  the  contemplation  of  works  of  human  art,  whether 
that  art  has  been  employed  in  material  things,  or  be  purely 
intellectual.  From  the  cottage  to  the  cathedral — from  the 
simplest  ballad  air,  to  the  harmony  of  a  choral  anthem — from 
a  pastoral  to  an  epic  poem  or  tragedy — from  a  landscape  to 
a  cartoon, — in  each  case  there  is  a  wide  interval,  and  you 
may  easily  perceive,  that,  merely  by  adding  what  seemed 
degree  after  degree,  you  arrive  at  last  at  emotions  which 
have  little  apparent  resemblance  to  the  emotions  with  which 
the  scale  began. 

In  the  moral  scene  the  progression  is  equally  evident. 
Let  us  suppose,  for  example,  that  in  the  famine  of  an  a;my, 
a  soldier  divides  his  scanty  allowance  with  one  of  his  com- 
rades, whose  health  is  sinking  under  the  privation.  We  feel 
in  the  contemplation  of  this  action,  a  pleasure,  which  is  that 
of  moral  beauty.  In  proportion  as  we  imagine  the  famine 
3* 


IS  TASTE. 

of  longer  duration,  or  the  prospect  of  relief  less  probable^ 
the  action  becomes  more  and  more  morally  grand  and  heroic. 
Let  us  next  imagine,  that  the  comrade,  to  whose  relief  the 
soldier  makes  this  generous  sacrifice,  is  one  whose  enmity 
he  has  formerly  experienced  on  some  interesting  occasion  j 
and  the  action  is  not  heroic  merely,  it  is  sublime. 

It  is  in  the  moral  conduct  of  our  fellow  men,  that  the  spe- 
cies of  sublimity  is  to  be  found,  which  we  most  gladly  re- 
cognise, as  the  character  of  that  glorious  nature,  which  we 
have  received  from  God, — a  character  which  makes  us  more 
erect  in  mind,  than  we  are  in  stature,  and  enables  us  not  to 
gaze  on  the  heavens  merely,  but  to  lift  to  them  our  very 
wishes,  and  to  imitate  in  some  faint  degree,  and  to  admire 
at  least,  where  we  cannot  imitate,  the  gracious  perfection 
that  dwells  there. — Brown. 

Questions. — 1.  What  illustration  is  given  of  the  emotions  of 
beauty  and  subUmity  which  arise  from  contemplating  the  works  of 
nature  ?  2.  Tlie  works  of  human  art  ?  3.  What  is  the  example  for 
illustrating  moral  beauty  and  sublimity  ? 


LESSON  10. 

Taste. 

Fhie  Arts,  the  arts  generally  distinguished  by  the  appellation  fine, 
are  poetry,  music,  painting,  sculpture,  and  engraving,  with 
their  several  branches.  To  these  may  be  added  architectur« 
and  gardening. 

The  word  taste  has  two  general  significations :  one  literal 
or  primitive  relating  to  corporeal  sensations ;  the  other  figu- 
rative, referring  to  mental  discernment.  This  metaphor 
would  not  have  been  so  general,  had  there  not  been  a  con- 
formity between  mental  taste,  and  that  sensitive  taste  which 
gives  us  a  relish  of  every  flavour.  The  subject  of  this  lesson 
•j^  mental  or  intellectual  taste. 

Without  the  emotions  of  beauty  and  sublimity,  there  would 
be  no  taste  to  discern  the  aptitude  of  certain  means  for  pro- 
ducing these  emotions.  On  the  other  hand,  w-ithout  the 
judgment,  which  discerns  this  order,  in  the  relations  of  means 
and  ends,  there  would  be  no  voluntary  adaptation  of  the 
groat  stores  of  forms  and  sounds,  and  colours,  for  producing 


TASTE. 


10 


them, — none  of  those  fine  arts  which  give  as  much  happi- 
ness as  embellishment  to  life.  Reason  and  good  sense  have 
so  extensive  an  influence  on  all  the  operations  and  decisions 
of  taste,  that  a  thorough  good  taste  may  well  be  considered 
as  a  power,  compounded  of  natural  sensibility  to  beauty, 
and  of  improved  understanding.  Frequent  exercise  and 
curious  attention  to  its  proper  objects  must  greatly  heighten 
its  power.  Nothing  is  more  improveable  than  that  part  of 
taste,  which  is  called  an  ear  for  music.  At  first,  the  sim- 
plest and  plainest  compositions  only  are  relished.  Our  plea- 
sure is  extended  by  use  and  practice,  which  teach  us  to  re- 
lish  finer  melody,  and  by  degrees  enable  us  to  enter  into  the 
intricate  and  compound  pleasures  of  harmony.  An  eye  for 
the  beauties  of  painting  is  never  acquired  all  at  once.  It  is 
gradually  formed  by  being  conversant  among  pictures,  and 
studying  the  works  of  the  best  masters.  It  is  the  same  with 
respect  to  the  beauty  of  composition  or  discourse  :  attention 
to  the  most  approved  models,  study  of  the  best  authors,  com- 
parisons of  lower  and  higher  degrees  of  the  same  beauties, 
operate  towards  the  refinement  of  taste. 

In  no  part  of  nature  is  the  pure  benevolence  of  ^Jeaven 
more  strikingly  conspicuous  than  in  our  susceptibility  of  the 
emotions  of  this  class.  In  consequence  of  these  emotions, 
it  is  scarcely  possible  for  us  to  look  around,  without  feeling 
either  some  happiness  or  some  consolation.  Sensual  plea- 
sures soon  pall,  even  upon  the  profligate,  who  seeks  them  in 
vain  in  the  means  which  were  accustomed  to  produce  them  ; 
weary,  almost  to  disgust,  of  the  very  pleasures  which  he 
seeks,  and  yet  astonished  that  he  does  not  find  them.  The 
labours  of  severer  intellect,  if  long  continued,  exhaust  the 
energy  which  they  employ ;  and  we  cease,  for  a  time,  to  be 
capable  of  thinking  accurately,  from  the  very  intentness  and 
accuracy  of  our  thought.  The  pleasures  of  taste,  however, 
by  their  variety  of  easy  delight,  are  safe  from  the  languor 
which  attends  any  monotonous  or  severe  occupation,  and, 
instead  of  palling  on  the  mind,  they  produce  in  .it,  with  the 
very  delight  which  is  present,  a  quicker  sensibility  to  future 
pleasure.  Enjoyment  springs  from  enjoyment ;  and  if  we 
have  not  some  deep  wretchedness  within,  it  is  scarcely  pos- 
sible for  us,  with  the  delightful  resources  which  nature  and 
art  present  to  us,  not  to  be  happy,  as  often  as  we  will  to  be 
happy. 


20  POETRY. 

Questions. — 1.  What  are  the  two  significations  of  the  word  taste  ^ 
2.  What  does  intellectual  taste  discern  ?  3.  How  may  a  thorough 
good  taste  be  considered  ?  4.  What  effect  have  exercise  and  atten- 
tion upon  taste  ?  5.  What  examples  of  this  are  given  P  6.  What  is 
said  of  sensual  pleasures  ?     7.  Of  the  pleasures  of  taste? 


LESSON  11. 

Poetry. 

The  object  of  the  philosopher  is  to  inform  and  enlighten 
mankind ;  that  of  the  orator,  to  acquire  an  ascendant  over 
the  will  of  others,  by  bending  to  his  own  purposes  their  judg- 
ments, their  imaginations,  and  their  passions  :  but  the  pri- 
mary and  the  distinguishing  aim  of  the  poet  is  to  jjlease  ;  and 
the  principal  resource  which  he  possesses  for  this  purpose, 
is  by  addressing  the  imagination. 

In  poetry,  we  perceive  every  where  what  Akenside  calls 

"The  charm, 
That  searchless  nature  o'er  the  sense  of  man 
Diffuses, — to  behold,  in  lifeless  tilings 
The  inexpressive  semblance  of  himself, 
Of  thought  and  passion." 

The  zephyrs  laugli, — the  sky  smiles, — the  forest  frowns, 
— the  storm  and  the  surge  contend  together, — the  solitary 
place  not  merely  blossoms  like  the  rose,  but  it  is  glad.  AU 
nature  becomes  animated.  The  poetic  genius,  like  that 
soul  of  the  world,  by  which  the  early  philosophers  accounted 
for  all  earthly  changes,  breathes  its  own  spirit  into  every 
thing  surrounding  it. 

The  world  is  full  of  poetry — the  air 
Is  living  with  its  spirit ;  and  the  waves 
Dance  to  the  music  of  its  melodies. 
And  sparkle  in  its  brightness — earth  is  veiled, 
And  mantled  with  its  beauty ;   and  the  walls, 
That  close  the  universe,  with  crystal,  in, 
Are  eloquent  with  voices,  that  proclaim 
The  unseen  glories  of  immensity. 


STUDY    OF    HISTORY.  i 

'Tis  not  the  chime  and  flow  of  words,  that  move  \ 
In  measured  file,  and  metrical  array ; 

'Tis  not  the  union  of  returning  sounds,  1 
Nor  all  the  pleasing  artifice  of  rhyme, 

And  quantity,  and  accent,  that  can  give  3 

This  all-pervading  spirit  to  the  ear,  i 

Or  blend  it  with  the  movings  of  the  souh  -i 

'Tis  a  mysterious  feeling,  which  combines  ' 

Man  with  the  world  around  him,  in  a  chain  ' 
Woven  of  flowers,  and  dipped  in  sweetness,  till 

He  taste  the  high  communion  of  his  thoughts,  \ 

With  all  existences,  in  earth  and  heaven,  ■ 

That  meet  him  in  the  charm  of  grace  and  power.  J 

'Tis  not  the  noisy  babbler,  who  displays,  ' 

In  studied  phrase  and  ornate  epithet,  \ 

And  rounded  period,  poor  and  vapid  thoughts,  ] 

Which  peep  from  out  the  cumbrous  ornaments,  i 

That  overload  their  littleness.    Its  words  i 

Are  few,  but  deep  and  solemn  ;  and  they  break  j 

Fresh  from  the  fount  of  feeling,  and  are  full  ; 

Of  all  that  passion,  which,  on  Carmel,  fired  j| 

The  holy  prophet,  when  his  lips  were  coals,  i 
His  language  winged  with  terror,  as  when  bolts  '  f^ 
Leap  from  the  brooding  tempest,  armed  with  wrath,  ^^  J 
Commissioned  to  affright  us,  and  destroy. — Percival.        j^ 

Questions. — 1.  What  is  the  object  of  the  philosopher  ?    2.  Of  ] 

the  orator  ?     3.  Of  the  poet  ?     4.  What  is  the  principal  resource  of         ■■ 

the  poet  ?    5.  To  what  is  the  poetic  genius  compared  ?  . 


LESSON  12. 

Advantages  of  studying  History. 

If  we  consider  the  knowledge  of  history  with  regard  to  its 
application,  we  shall  find  that  it  is  eminently  useful  to  us  in 
three  respects,  namely,  as  it  appears  in  a  moral,  a  political, 
and  a  religious  point  of  view. 

In  a  moral  point  of  view,  it  is  beneficial  to  mankind  at  large, 
as  the  guide  of  their  conduct.  In  a  political — as  it  suggests 
useful  expedients  to  those  who  exercise  the  public  offices  of 


SSS  STUDY    OF    HISTORY.  1 

the  State ;  or  as  it  enables  us  to  form,  by  comparison  witli     ' 

those  who  have  gone  before  them,  a  just  estimate  of  their    I 

merits.  In  a  religious — as  it  teaches  us  to  regard  the  Supreme    | 

Being  as  the  governor  of  the  universe,  and  sovereign  disposer    \ 

of  all  events.  1 

The  faculties  of  the  soul  are  improved  by  exercise ;  and    ; 

nothing  is  more  proper  to  enlarge,  to  quicken,  and  to  refine    \ 

them,  than  a  survey  of  the  conduct  of  mankind.     History    ] 

supplies  us  with  a  detail  of  facts,  and  submits  them  to  exami-    , 

nation  before  we  are  called  into  active  life.     By  observation   \ 

and  reflection  upon  others  we  begin  an  early  acquaintance    \ 

with  human  nature,  extend  our  views  of  the  moral  world,  and    ' 

are  enabled  to  acquire  such  a  habit  of  discernment,  and  cor-   "i 

rectness  of  judgment,  as  others  obtain  only  by  experience.  ] 

By  meditating  on  the  lives  of  sages  and  heroes,  we  exercise  j 

our  virtues  in  a  review,  and  prepare  them  for  approaching  ac-  I 

tion.     We  learn  the  motives,  the  opinions,  and  the  passions  1 

of  the  men  who  lived  before  us ;  and  the  fruit  of  that  study  is  1 

a  more  perfect  knowledge  of  ourselves,  and  a  correction  of   \ 

our  failings  by  their  examples.  ^ 

Experience  and  the  knowledge  of  history  reflect  nmtual  ^ 

light,  and  afford  mutual  assistance.     Without  the  former  no  j 

one  can  act  with  address  and  dexterity.     Without  the  latter  . 

no  one  can  add  to  the  natural  resources  of  his  own  mind  a  \ 

knowledge  of  those  precepts  and  examples,  which  have  tended  ] 

to  form  the  character  and  promote  the  glory  of  eminent  m.en.  j 

History  contributes  to  divest  us  of  many  illiberal  prejudices,  ] 

by  enlarging  our  acquaintance  with  the  world.     It  sets  us  at  ; 

liberty  from  that  blind  partiality  to  our  native  country,  which  ] 

is  a  sure  mark  of  a  contracted  mind,  when  due  merit  is  not  " 

allowed  to  any  other.  This  study  likewise  tends  to  strengthen  ; 

our  abhorrence  of  vice  ;  and  creates  a  relish  for  true  greatness  i 

and  solid  glory.    We  see  the  hero  and  the  philosopher  repre-  | 

sented  in  their  proper  colours ;  and  as  magnanimity,  honour,  1 

integrity,  and  generosity,  when  displayed  in  illustrious  in-  J 

stances,  naturally  make  a  favourable  impression  on  our  minds,  ; 

our  attachment  to  them  is  gradually  formed.     The  fire  of  j 

enthusiasm  and  of  virtuous  emulation  is  lighted,  and  we  long  \ 

to  practise  what  we  have  been  instructed  to  approve.  j 

The  love  of  our  country  naturally  awakens  in  us  a  spirit  of  ; 

curiosity  to  inquire  into  the  conduct  of  our  ancestors,  and  to  ] 

learn  the  memorable  events  of  their  history.     Nothing  that  -l 


PHILOSOPHY. 


happened  to  them  can  be  a  matter  of  indifference  to  us.  We 
are  their  descendants,  we  reap  the  fruits  of  their  public  and 
private  labours,  and  we  not  only  share  the  inheritance  of 
their  property,  but  derive  reputation  from  their  noble  actions. 
History,  considered  with  respect  to  the  nature  of  its  sub- 
jects, may  be  divided  into  general  trnd  particular ;  and  with 
respect  to  time,  into  ancient  and  modern.  Ancient  history 
commences  with  the  creation,  and  extends  to  the  reign  of 
Charlemagne,  in  the  year  of  our  Lord  eight  hundred.  Modern 
history,  beginning  with  that  period,  reaches  down  to  the  pre- 
sent times.  General  history  relates  to  nations  and  public  af- 
fairs, and  may  be  subdivided  into  ecclesiastical  and  civil,  or  ac- 
cording to  some  writers,  into  sacred  and  profane.  Biography, 
memoirs,  and  letters,  constitute  particular  history.  Statis'tics 
refer  to  the  present  condition  of  nations.  Geography  and 
chronology  are  important  aids,  and  give  order,  regularity,  and 
clearness  to  all.  Kett. 

Questions. — 1.  What  is  the  advantage  of  history  in  a  moral  point 
of  view  ?  2.  In  a  political  .^  3.  In  a  religious?  4.  What  are  the  uses 
of  history  in  respect  to  the  mental  facuhies  and  the  conduct  of  life  ? 
5.  How  does  history  divest  us  of  illiberal  prejudices  ?  G.  How  does 
it  tend  to  strengthen  our  abhorrence  of  vice,  and  create,  a  relish  for 
true  greatness  ?  7.  What  is  said  of  the  history  of  our  ancestors  ? 
8.  How  may  history  be  divided  .''     9.  subdivided  ? 


LESSON  13. 

PhilosopTiy . 

Proposi'tion,  a  sentence  in  which  any  thing  is  affirmed  or  denied. 
Demonstra'tion,  a  process  of  reasoning  in  which  we  perceive  it 

to  be  impossible  that  the  conclusion  should  not  follow  from  the 

premises,  or  antecedent  propositions. 

By  philosophy  we  mean  the  knowledge  of  the  reasons  of 
things,  in  opposition  to  history,  which  is  the  bare  knowledge 
of  facts ;  or  to  mathematics,  which  is  the  knowledge  of  the 
quantity  of  things,  or  their  measures.  These  three  kinds  of 
knowledge  ought  to  be  joined  as  much  as  possible.  History 
furnishes  matter,  principles,  and  practical  examinations,  and 
mathematics  complete  the  evidence.  All  arts  have  their  pe- 
culiar philosophy,  which  constitutes  their  theory.  It  is  to  be 
observed,  that  the  bare  intelligence  and  memory  of  philoso- 


24  PHILOSOPHY. 

phical  proposi'tions,  without  an  ability  to  demo'nstrate  them, 
is  not  philosophy,  but  history  only.  Where  such  propositions, 
however,  are  determinate  and  true,  they  may  be  usefully  ap- 
plied in  practice,  even  by  those  who  are  ignorant  of  their  de- 
monstrations. 

Philosophy  discovers  and  teaches  those  principles  by  means 
of  which  happiness  may  be  acquired,  preserved,  and  increased. 
Wisdom  applies  these  principles  to  the  benefit  of  individuals 
and  of  society.  Knowledge  which  is  applicable  to  no  useful 
purpose  cannot  deserve  the  name  of  wisdom.  The  sources 
of  that  knowledge  of  truth  which  leads  to  the  possession  of 
happiness  are  reason  and  revelation.  To  instruct  men  in 
those  truths  which  God  hath  communicated  to  mankind  by 
revelation,  is  the  province  of  theology.  To  teach  them  such 
truths,  connected  with  their  happiness,  as  are  capable  of 
being  discovered  by  the  powers  of  reason,  is  the  province  of 
philosophy. 

The  leading  offices  of  philosophy  may  be  easily  deduced 
from  the  general  idea  of  its  object.  As  the  permanent  en- 
joyment of  real  good  is  the  end  to  be  attained,  the  business 
of  philosophy,  therefore,  will  be  to  cultivate  the  understand- 
ing, and  direct  its  operations ;  to  correct  and  improve  the 
will  and  affections ;  to  inquire  out  the  causes  of  natural  ap- 
pearances, and  hence  arrive  .at  the  knowledge  of  the  first 
cause,  under  those  characters  and  relations  that  are  most 
interesting  to  mankind  ;  to  conduct  men  to  such  an  acquaint- 
ance with  the  properties  of  natural  bodies,  and  their  recipro- 
cal actions,  as  shall  enable  them  to  apply  the  objects  around 
them  to  their  own  convenience ;  and,  finally,  to  assist  them 
in  investigating  the  principles  of  social  virtue,  and  thus  pro- 
vide themselves  with  such  rules  of  conduct  as  arise  from  mu- 
tual convenience  and  interest,  from  the  natural  sentiments 
of  justice  and  humanity,  and  from  the  voluntary  engagements 
of  civil  society. 

Questions. — 1.  What  is  meant  by  philosophy  ?  2.  What  three 
kinds  of  knowledge  should  be  joined  as  much  as  possible?  3.  What 
is  the  distinction  between  philosophy  and  wisdom  ?  4.  What  is  the 
province  of  theology  ?  5.  Of  philosophy  ?  6.  What  are  the  leading 
offices  of  philosophy  ?  Note.  The  three  great  objects  of  philosophy 
are  God,  man,  arid  the  universe.  Philosophy  is  sometimes  divided 
into  three  parts,  intellectual,  moral,  and  physical,  or  natural. 


I>RAISE    0^   PHILOSOPHY.  <15 


LESSON  i4 


The  Praise  of  Philosophy. 

But  now  !et  other  themes  our  care  engage^ 

For  lo,  with  modest  yet  majestic  grace, 
To  curb  imagination's  lawless  rage, 

And  from  within  the  cherish'd  heart  to  brace. 
Philosophy  appears.     The  gloomy  race 

By  Indolence  and  moping  Fancy  bred, 
Fear,  Discontent,  Solicitude,  give  place, 

And  Hope  and  Courage  brighten  in  their  stead, 

While  on  the  kindling  soul  her  vital  beams  are  shed 

Then  waken  from  long  lethargy  to  life 

The  seeds  of  happiness  and  powers  of  thought ; 
Then  jarring  appetites  forego  their  strife, 

A  strife  by  ignorance  to  madness  wrought. 
Pleasure  by  savage  man  is  dearly  bought 

With  fell  revenge,  lust  that  defies  control, 
With  gluttony  and  death.     The  mind  untaught 

Is  a  dark  waste,  where  fiends  and  tempests  howl ; 

As  Phoebus  to  the  world,  is  science  to  the  soul. 

And  Reason  now  through  number,  time,  and  space, 
Darts  the  keen  lustre  of  her  serious  eye, 

And  learns,  from  facts  compared,  the  laws  to  trace, 
Whose  long  progression  leads  to  Deity. 

Can  mortal  strength  presume  to  soar  so  high ! 
Can  mortal  sight,  so  ok  bedimm'd  with  tears 

^uch  glory  bear ! — for  lo,  the  shadows  fly 
From  Nature's  face ;  confusion  disappears. 
And  order  charms  the  eyes,  and  harmony  the  ears 

|n  the  deep  windings  of  the  grove,  no  more 

The  hag  obscene  and  grisly  phantom  dwell ; 
)Kor  in  the  fall  of  mountain-stream,  or  roar 

Of  winds,  is  heard  the  angry  spirit's  yell ; 

No  wizard  mutters  the  tremendous  spell, 
f^or  sinks  convulsive  in  prophetic  swoon ; 

Nor  bids  the  noise  of  drums  and  trumpets  swell, 
Vo  ease  of  fancied  pangs  the  labouring  moon, 

Or  chase  the  shade  that  blots  the  blazing  wb  of  noon 
3 


SS6  PRAISE    OP  PHILOSOPHY. 

Many  a  long-lingering  year,  in  lonely  isle, 

Stunn'd  with  th'  eternal  turbulence  of  waves, 
Lo,  with  dim  eyes,  that  never  learn'd  to  smile,  "g/ 

And  trembling  hands,  the  famish'd  native  craves 
Of  Heaven  his  wretched  fare :  shivering  in  caves, 

Or  scorch'd  on  rocks,  he  pines  from  day  to  day : 
But  Science  gives  the  word ;  and  lo,  he  braves 

The  surge  and  tempest,  lighted  by  her  ray, 

And  to  a  happier  land  wafts  merrily  away. 

And  even  where  nature  loads  the  teeming  plains 

With  the  full  pomp  of  vegetable  store, 

Her  bounty  unimproved  is  deadly  bane : 
Dark  woods,  and  rankling  wilds,  from  shore  to  shore, 
Stretch  their  enormous  gloom  ;  which  to  explore 

Even  Fancy  trembles  in  her  sprightliest  mood ; 
For  there,  each  eye-ball  gleams  with  lust  of  gore, 

Nestles  each  murderous  and  each  monstrous  brood. 

Plague  lurks  in  every  shade,  and  steams  from  every  flood. 

'Twas  from  Philosophy  man  learn'd  to  tame 

The  soil  by  plenty  to  intemperance  fed. 
Lo,  from  the  echoing  axe,  and  thundering  flame, 

Poison,  and  Plague,  and  yelling  Rage  are  fled. 
The  waters  bursting  from  their  slimy  bed, 

Bring  health  and  melody  to  every  vale  : 
And  from  the  breezy  main,  and  mountain's  head, 

Ceres  and  Flora  to  the  sunny  dale. 

To  fan  their  glowing  charms,  invite  the  flutt'ring  gale. 

What  dire  necessities  on  every  hand 

Our  art,  our  strength,  our  fortitude  require  ! 

Of  foes  intestine  what  a  numerous  band 
Against  this  little  throb  of  life  conspire ! 

Yet  Science  can  elude  their  fatal  ire  i 

Awhile,  and  turn  aside  death's  levell'd  dart. 

Sooth  the  sharp  pang,  allay  the  fever's  fire,  f 

And  brace  the  nerves  once  more,  and  cheer  the  heart, 
And  yet  a  few  soft  nights  and  balmy  days  impart. 

Nor  less  to  regulate  man's  moral  frame 

Science  exerts  her  all-composing  sway. 
Flutters  thy  breast  with  fear,  or  pants  for  fame, 

Or  pines,  to  Indolence  and  Spleen  a  prey, 


GENEitAt   PROPERTIES    OP    BOfiilES. 


at 


Or  Avarice,  a  fiend  more  fierce  than  they  ? 
Flee  to  the  shade  of  Academus'  grove ; 

Where  Cares  molest  not,  Discord  melts  away 
In  harmony,  and  the  pure  passions  prove 
How  sweet  the  words  of  Truth  breathed  from  the  lips  of 
Love. 

What  cannot  Art  and  Industry  perform, 

When  Science  plans  the  progress  of  their  toil ! 

They  smile  at  penury,  disease,  and  storm ; 
And  oceans  from  their  mighty  mounds  recoil. 

When  tyrants  scourge,  or  demagogues  embroil 
A  land,  or  when  the  rabble's  headlong  rage 

Order  transforms  to  anarchy  and  spoil, 
Deep-versed  in  man,  the  philosophic  sage 
Prepares  with  lenient  hand  their  frenzy  to  assuage. 

'Tis  he  alone,  whose  comprehensive  mind, 

From  situation,  temper,  soil,  and  clime 
Explored,  a  nation's  various  powers  can  bind 

And  various  orders,  in  one  form  sublime 
Of  polity,  that  midst  the  wrecks  of  time. 

Secure  shall  lift  its  head  on  high,  nor  fear 
Th'  assault  of  foreign  or  domestic  crime, 

;  While  public  Faith,  and  public  Love  sincere, 

And  Industry  and  Law  maintain  their  sway  severe. 

Beattib. 


LESSON  15.  j 

General  Properties  of  Bodies. 

Symmetrical,  proportionate,  having  parts  well  adapted  to  each 

other,  i 

Cap'illary,  a  term  applied  to  tubes  of  a  very  small  bore,  scarcely  ^ 

larger  than  to  admit  a  hair,  derived  from  capillus,  the  Latin  ] 

word  for  hair.  ■ 

When  we  speak  of  bodies,  we  mean  substances,  of  what-  \ 
ever  nature,  whether  solid  or  fluid ;  and  matter  is  the  ge-  ■ 
neral  term  used  to  denote  the  substance  of  which  the  diffe- 
rent bodies  are  composed.     As  we  do  not  suppose  any  body  ; 


2ft  GENERAL    PROPERTIES    OF    BODIES. 

to  exist  without  certain  properties,  such  as  impenetrability, 
extension,  figure,  divisibility,  inertness,  and  attraction,  these, 
therefore,  are  called  the  general  properties  of  bodies. 

By  impenetrability ,  is  meant  the  property  which  bodies 
have  of  occupying  a  certain  space,  so  that,  where  one  body 
is,  another  cannot  be,  without  displacing  the  former  ;  for  two 
bodies  cannot  exist  in  the  same  place  at  the  same  time.  A 
liquid  may  be  more  easily  removed  than  a  solid  body  ;  yet  it 
is  not  the  less  substantial,  since  it  i?  as  impossible  for  a 
liquid  and  a  solid  to  occupy  the  same  space  at  the  same  time, 
as  for  two  solid  bodies  to  do  so.  If  some  water  be  put  into 
a  tube  closed  at  one  end,  and  a  piece  of  wood  be  inserted 
that  accurately  fits  the  inside  of  the  tube,  it  will  be  impos- 
sible to  force  the  wood  to  the  bottom,  unless  the  water  is 
first  taken  away.  The  air  is  a  fluid  differing  in  its  nature 
from  liquids,  but  not  less  impenetrable.  If  you  endeavour 
to  fill  a  phial  by  immersing  it  in  water,  the  air  will  rush  out 
in  bubbles  in  order  to  make  way  for  the  water ;  and  if  you 
reverse  the  phial,  and  plunge  it  perpendicularly  into  the  wa- 
ter, so  that  the  air  will  not  be  able  to  escape,  the  water  will 
not  fill  it,  though  it  will  rise  a  little,  because  it  compresses 
the  air  into  a  smaller  space  in  the  upper  part  of  the  glass. 

A  body  which  occupies  a  certain  space  must  necessarily 
have  extension ;  that  is  to  say,  length,  breadth,  and  depth. 
These  are  called  the  dimensions  of  extension,  and  we  can- 
not form  ail  idea  of  any  body  without  them.  The  limits  of 
extension  are  called  figure  or  shape.  A  body  having  length, 
breadth,  and  depth,  cannot  be  without  form,  either  symme- 
trical or  irregular  ;  and  this  property  admits  of  almost  an  in- 
finite variety.  The  natural  form  of  mineral  substances  is 
that  of  crystals ;  many  of  them  are  very  beautiful,  and  not 
less  remarkable  for  their  transparency  and  colour,  than  for 
their  perfect  regularity,  as  may  be  seen  in  the  various  mu- 
seums and  collections  of  natural  history.  The  vegetable 
and  animal  creation  appears  less  symmetrical,  but  is  still 
more  diversified  in  figure  than  the  mineral  kiji^dpm.  Mfc^^ 
nufactured  substances  assume  the  various  arbitrary  f<^ms  . 
which  the  art  of  man  designs  for  them. 

Divisibility  is  that  property  of  matter,  by  which  its  parts 
may  be  divided  and  separated  from  each  other ;  and  of  this 
division  there  can  be  no  end.  We  can  never  conceive  of  a 
particle  of  matter  so  small  as  not  to  have  an  upper  and  under 


GENERAL    PROPERTIES    OF    BODIES.  29 

surface,  which  might  be  separated,  if  we  had  instruments 
fine  enough  for  the  purpose.  A  grain  of  gold  may  be  ham- 
mered by  the  gold-beaters  to  such  a  degree  of  fineness,  that 
the  two  millionth  part  of  it  may  be  seen  by  the  naked  eye ; 
and  by  the  help  of  a  microscope  the  fifty  millionth  part  will 
be  visible.  There  are  animals,  it  is  said,  so  small  that  a 
single  grain  of  sand  is  larger  than  four  millions  of  them. 
But  the  natural  divisions  of  matter  are  still  more  wonderful. 
The  fragrance  of  a  body  is  a  part  of  the  body  itself,  and  is 
produced  by  very  minute  particles  or  exhalations  which 
escape  from  it.  How  inconceivably  small  must  be  the  odo- 
riferous particles  of  a  carnation,  which  diffuse  themselves 
through  a  whole  garden,  so  that,  in  every  part  of  it,  its  fra- 
grance is  perceptible ! 

The  word  inertness  expresses  the  resistance  which  inac- 
tive matter  makes  to  a  change  of  state.  It  requires  some 
external  force  to  put  a  body  which  is  at  rest  in  motion ;  and 
an  exertion  of  strength  is  also  requisite  to  stop  a  body  which 
is  already  in  motion.  If  a  ball  were  fired  from  a  cannon  with 
a  certain  velocity,  and  there  were  no  resistance  from  the  air, 
it  would  circulate  round  the  earth  perpetually,  and  never 
come  to  a  state  of  rest.  In  this  manner  the  moon  goes 
round  the  earth. 

By  attraction  is  meant  the  tendency  that  bodies  have  to 
approach  each  other,  whatever  be  the  cause  of  such  tenden- 
cy. All  bodies  are  composed  of  infinitely  small  particles 
of  matter,  each  of  which  possesses  the  power  of  attracting 
or  drawing  towards  itself  any  other  particle,  and  of  uniting 
with  it,  when  sufficiently  near  to  be  within  the  influence  of 
its  attraction ;  but  in  minute  particles  this  power  extends  t® 
so  very  small  a  distance  around  them  that  its  eflfect  is  not 
sensible,  unless  they  are,  or  at  least  appear  to  be,  in  contact. 
It  then  makes  them  adhere  together,  and  is  hence  called  the 
attraction  of  cohesion.  It  is  by  this  principle  that  bodies 
preserve  their  forms,  and  are  prevented  from  falling  to 
pieces.  The  cohesive  attraction  of  solids  is  much  greater 
than  that  of  fluids ;  and  in  elastic  fluids,  such  as  air,  there 
is  no  cohesive  attraction  among  the  particles,  and  the  utmost 
efforts  of  human  art  have  proved  ineffectual  in  the  attempt 
to  compress  them,  so  as  to  bring  them  within  the  sphere  of 
each  other's  attraction,  and  make  them  cohere.  If  two  po- 
lished plates  of  marble,  or  of  brass  be  but  together  with  a 
3* 


30  ATTRACTION    OF    GRAVITATION. 

little  oil  between  them  to  fill  up  the  pores  in  their  surfaces, 
they  will  cohere  so  powerfully  as  to  require  a  very  consi- 
derable force  to  separate  them.  Two  globules  of  quicksil- 
ver, placed  very  near  to  each  other,  will  run  together,  and 
drops  of  water  will  do  the  same.  The  ascent  of  water  and 
other  liquids  in  sugar,  sponge,  and  all  porous  bodies  is  a  spe- 
cies of  this  attraction,  and  is  called  capillary  attraction. 

Some  bodies  appear  to  possess  a  power  which  is  the  re- 
verse of  the  attraction  of  cohesion.  It  is  called  repulsion, 
and  is  supposed  to  extend  to  a  small  distance  around  bodies, 
so  as  to  prevent  them  from  coming  into  actual  contact. 
Water  repels  most  bodies  till  they  are  wet.  A  small  needle 
carefully  placed  on  water  will  float.  The  drops  of  dew 
which  appear  in  the  morning  on  plants  assume  a  globular 
form,  from  the  mutual  attraction  between  the  particles  of 
V4^ater;  and  upon  examination  it  will  be  found  that  the  drops 
do  not  touch  the  leaves,  for  they  roll  off  in  compact  bodies, 
which  would  not  be  the  case  if  there  existed  any  degree  of 
attraction  between  the  water  and  the  leaf.  The  repelling 
force  between  water  and  oil  is  so  great  that  it  is  impossible- 
to  mix  them  in  such  a  manner  that  they  shall  not  separate 
again. 

Questions. — 1.  What  is  matter  ?  2.  What  are  the  general  pro- 
perties of  bodies  ?  3.  What  is  impenetrability  ?  4.  By  what  experi- 
ments is  this  property  of  matter  illustrated  ?  5.  Define  extension  and 
figure.  6.  What  is  divisibility,  and  liow  illustrated  ?  7,  Define  inert- 
ness ?  8.  What  is  meant  by  attraction  ?  9.  Attraction  of  cohesion  ? 
10.  What  is  said  of  the  attraction  of  solids  and  fluids  ?  11.  What  ex- 
periments illustrate  cohesive  attraction  .'  12.  What  is  capillary  at- 
traction.' 13.  What  is  repulsion,  and  by  what  experiments  illua- 
Uftted. 


LESSON   16, 

Attraction  of  Gravitation. 

Roctilin'ear,  consisting  of  right  or  straight  lines. 
Curvilin'ear,  consisting  of  crooked,  or  curved  lines. 
Projec'tile,  a  body  put  in  motion. 
Evaga'tion,  a  wandering  deviation. 
Phenom'enon,  (pi.  phenomena)  appearance^  commonly  oxprossivc 
of  some  remarkable  appearance  in  nature. 

The  attraction  of  gravitation  is  only  a  modification  of  the  j 


ATTRACTION    Of    GRAVITATION.  31 

attraction  of  cohesion.  The  latter  is  not  perceptible  but  in 
very  minute  particles,  and  at  very  small  distances,  the  other 
acts  on  the  largest  bodies,  and  extends  to  immense  distances. 

That  very  law  which  moulds  a  tear, 

And  bids  it  trickle  from  its  source, 

That  law  preserves  the  earth  a  sphere. 

And  guides  the  planets  in  their  course. — Rogers. 

The  tendency  which  bodies  have  to  fall  is  produced  en- 
tirely by  the  attraction  of  the  earth  ;  for  the  earth  is  so  much 
larger  than  any  body,  on  its  surface,  that  it  forces  every 
body,  which  is  not  supported,  to  fall  upon  it.  The  follov/ing 
simple  incident  led  to  the  most  extensive  and  complicated 
calculations,  and  was  productive  of  the  most  noble  and  won- 
derful discoveries.  Newton  happening  one  day,  in  the  year 
1666,  when  only  twenty-five  years  of  age,  to  be  sitting  under 
an  apple-tree,  and  an  apple  falling  upon  his  head,  it  suggested 
a  variety  of  reflections.  The  phenomena  of  falling  bodies 
in  particular  engaged  his  attention ;  and,  extending  his  re- 
searches to  the  heavens,  he  began  to  investigate  the  nature 
of  motion  in  general.  Because  there  is  motion,  he  reason^ 
ed,  there  must  be  a  force  that  produces  it.  But  what  is  this 
force  1  That  a  body  when  left  to  itself,  will  fall  to  the  ground, 
is  known  to  the  most  ignorant ;  but  if  you  ask  them  the  rea- 
son of  its  thus  falling,  they  will  think  you  either  an  idiot  or ' 
a  madman.  The  circumstance  is  too  common  to  excite  their 
wonder,  although  it  is  so  embarrassing  to  philosophers,  that 
they  think  it  almost  inexplicable.  It  is  the  mark  of  a  supe- 
rior genius  to  find  matter  for  wonder,  observation,  and  re- 
search, in  circumstances  which  to  the  ordinary  mind  appear 
trivial,  because  they  are  common,  and  with  which  they  are 
satisfied,  because  they  are  natural,  without  reflecting  that 
nature  is  our  grand  field  of  observation,  that  within  it  is  con- 
tained our  whole  store  of  knowledge ;  in  a  word,  that  Us 
study  the  works  of  nature,  is  to  learn  to  appreciate  and  ad- 
mire the  wisdom  of  God. 

In  applying  his  reflections  on  the  nature  of  falling  bodies 
to  the  celestial  motions,  Newton  soon  perceived  that  the 
force  of  gravity  was  not  confined  to  the  surface  of  our  globe  ; 
it  being  found  to  act  alike  at  the  bottom  of  the  lowest  valleys, 
jind  at  the  summit  of  the  most  lofty  mountains.    This  led 


32  ATTRACTION    OF    GRAVITATION. 

him  to  conjecture,  that  it  might  extend  as  far  as  the  qjoon, 
and  be  the  means  of  retaining  her  in  her  orbit.  Imagine 
the  moon,  he  reasoned,  at  the  first  moment  of  its  creation, 
to  have  been  projected  forward,  with  a  certain  velocity,  in  a 
rectilinear  direction  ;  then,  as  soon  as  it  began  to  move,  gra- 
vity would  act  upon  it,  an<l  impel  it  toward  the  centre  of  the 
earth.  But  as  a  body,  impelled  by  two  forces,  will  follow  the 
direction  of  neither,  the  moon,  so  circumstanced,  would 
neither  proceed  directly  forward,  nor  fall  directly  downward, 
but  keep  a  middle  course,  and  move  round  the  earth  in  a 
curvilinear  orbit.  This  may  be  more  fully  illustrated,  by  at- 
tending to  the  motion  of  a  shot,  or  any  other  projectile.  A 
ball,  shot  from  the  mouth  of  a  cannon,  in  a  horizontal  direc- 
tion, does  not  fall  to  the  ground  till  it  has  proceeded  to  a 
considerable  distance ;  and  if  it  be  discharged  from  the  top 
of  a  high  mountain,  it  will  fly  still  further  before  it  comes  to 
the  earth.  Increase  the  force  and  the  height,  and  the  dis- 
tance will  be  augmented  accordingly.  And  thus,  in  imagi- 
nation at  least,  we  can  suppose  the  ball  to  be  discharged 
with  such  velocity,  that  it  will  never  come  to  the  ground, 
but  return  to  the  place  whence  it  set  out,  and  circulate  con- 
tinually round  the  earth,  in  the  manner  of  a  little  moon. 
Thus  proceeding  in  his  reflections,  Newton  discovered  the 
admirable  provision  of  the  great  Creator  to  prevent  the  eva- 
gation  of  the  planets,  and  to  retain  them  exactly  within  the 
.bounds  of  tlieir  orbits.  This  he  has  demonstrated  to  be  ef- 
fected by  gravity^  and  that  gravity  and  motion  completely 
solve  all  the  phenomena  of  the  planetary  revolutions,  both 
primary  and  secondary.  By  establishing  this  one  principle 
in  philosophy  he  has  fully  explained  the  system  of  the  world, 
so  far  as  it  relates  to  this  globe,  and  to  all  the  rest  of  the  pla- 
nets that  regard  the  sun  as  their  centre.  Such  is  the  New^ 
tonian  system  of  universal  gravitation  or  attraction.  But 
what  is  this  principle,  which  gives  life  and  motion  to  inani- 
mate beings,  and  how  does  it  act  ?  The  effbcts  are  visible, 
but  the  agent  that  produces  them  is  hidden  from  our  senses. 
It  eluded  the  search  of  Newton  himself;  he  that  soared  to 
the  utmost  regions  of  space,  and  looked  through  nature  with 
the  eye  of  an  eagle,  was  unable  to  discover  it.  This  princi- 
ple of  gravitation,  has  been  styled  "  The  constant  impression 
of  Divine  power ;" — in  every  other  sense  the  cause  is  likely 
to  continue  unexplored  by  man.     It  is,  however,  pretty  ge- 


CENTRE    OF    GRAVITY.  J^ 

nerally  agreed  that  the  same  principle  of  gravity,  by  whicll 
we  see  all  bodies  tend  toward  the  centre  of  the  earth,  is  m 
general  law  of  nature,  extended  to  all  distances,  and  to  every 
body,  or  substance,  in  the  universe. 

For  this  the  moon  thro'  heaven's  blue  concave  glides, 

And  into  motion  charms  th'  expanding  tides, 

While  earth  impetuous  round  her  axle  rolls. 

Exalts  her  wat'ry  zone,  and  sinks  the  poles. — Falconer. 

Questions. — 1.  What  is  the  attraction  of  gravitation  ?  2.  How 
i«  the  tendency  of  bodies  to  fall  produced  ?  3.  Wliat  incident  led 
Newton  to  the  most  wonderful  discoveries  ?  4.  How  did  he  reason  ? 
5.  What  is  considered  the  mark  of  a  superior  genius  ?  6.  What  did 
Newton  soon  perceive  respecting  the  force  of  gravity  ?  7.  What  did 
this  lead  him  to  conjecture  ?  8.  How  did  he  reason  respecting  the 
moon?  9.  What  had  this  principle  of  gravitation  been  styled?  10. 
What  did  Newton  fullj{^xplain  by  it  ? 


LESSON  17. 

Centre  of  Gravity. 

Perpendic'ularly ,  in  the  direction  of  a  straight  line  up  and  down. 
Pyr'amid,  a  pillar  ending  in  a  point. 

The  centre  of  gravity  of  a  body  is  that  point  about  which 
all  its  parts,  in  any  situation  exactly  balance  each  other,  so 
that  if  a  body  be  suspended  or  supported  by  this  point,  it  will 
rest  in  any  position.  Whatever  supports  the  centre  of  gra- 
vity bears  the  weight  of  the  whole  body  ;  and  while  it  is  sup- 
ported the  body  cannot  fall.  We  may  consider,  therefore, 
the  whole  weight  of  a  body  as  centered  in  this  point.  If  a 
line  is  drawn  from  the  centre  of  gravity  of  a  body,  perpen- 
dicularly to  the  horizon,  it  is  called  the  line  of  direction; 
because  it  is  the  line  whicti  the  centre  of  gravity  would  de- 
scribe, if  the  body  fell  freely.  The  broader  the  base  is 
upon  which  a  body  rests,  the  more  difficult  it  will  be  to  over- 
turn it,  as  it  must  bo  moved  the  more  to  bring  the  line  of 
direction  beyond  the  base.  A  cask  is  easily  rolled  along, 
and  so  is  a  ball,  but  a  box  is  moved  with  greater  difficulty. 
When  a  box  is  longer  than  it  is  broad,  it  is  much  more  easily 
turned  on  its  side  than  set  on  its  end.     A  building  in  tho 


dm'-  CENTRE    OF    GRAVITY. 

form  of  a  pyramid  is  the  most  durable,  because,  as  it  becomes  | 

narrower  and  narrower  as  it  ascends,  each  stone  or  brick  is  \ 
supported  by  those  below.     The  pyramids  of  Egypt,  both 

great  and  small,  still  remain,  and  without  doubt  will   do  so  ; 

for  thousands  of  years  to  come,  while  the  vast  temples  are  : 

crumbling  into  ruin.     In  building,  care  is  taken  not  to  bring  ; 

the  upper  rows  of  bricks   beyond   those   below,  and  for  this  i 

purpose  a  line  and  plummet  are  used.     But  it  does  not  follow,  i 

because  a  building  leans,  that  the  centre  of  gravity  does  not  I 

fall  within  the  base.     There  is  a  high  tower  at  Pisa,  a  town  j 

in  Italy,  which  leans  fifteen  feet  out  of  a  perpendicular  di-  ^ 
rection ;  strangers  tremble  to  pass  by  it,  still  it  is  found  by 

experiment  that  the  line  of  direction  falls  within  the  base^  ^ 

and  therefore  it  will  stand  while  its  materials  hold  together.  \ 

The  higher  the  centre  of  gravity  is,  the  more  easily  may  a  1 

body  be  overturned.     Hence,  a  wagon  or  cart  with  a  high  ^ 

load  is  more  in  danger  of  being  overturned  than  one  with  a  *j 

heavy  load  laid  lower.     This  proves  the  injurious  effect  of  ] 

rising  in  a  coach  or  boat  in  danger  of  oversetting,  the  centre  i 

of  gravity  being  thereby  raised,   and  the  line  of  direction  .i 

thrown  out  of  the  base.     In  such  circumstances  the  proper  ] 

course  is  to  lie  down  in  the  bottom,  so  as  to  bring  the  line  of  ] 

direction,  and  consequently  the  centre  of  gravity,  within  the  : 

base,  and  thus  remove   the   danger  of  oversetting.     Rope-  ^ 

dancers  perform  astonishing  feats  by  the  assistance  of  a  long  ' 
pole  with  very  weighty  pieces  of  lead  at  each  end,  by  which 

they  balance  themselves  and  recover  firm  footing,  if  likely  to  1 
fall  on  either  side.     In  our  ordinary  actions  we  regulate  the 

motions  of  our  bodies,  as  if  we  were  most  correctly  studying  j 

the  nature  and  effects  of  the  centre  of  gravity.     If  a  man  i 
wishes  to  rise  from  a  chair,  he  throws  his  body  forward.     If 

he  is  likely  to  fall  on  one  side  he  leans  to  the  other.     A  cor-  ; 

rect  knowledge  of  the  centre  of  gravity  in  bodies  is  of  the  i 
utmost  importance  in  the  science  of  mechanics,  as  well  as  in 

many  of  the  common  actions  of  life.  l 

Questions. — 1.  What  is  the  centre  of  gravity  ?    2.  The  line  of  \ 
direction?     3.  When  does  a  body  stand  most  firmly?     4.  Why  is  a 

pyramid  the  most  durable  form  of  building  ?     5.  What  occasions  a  ■ 

body  to  be  easily  overturned  ?     C.  What  is  the  proper  course  when  a  ; 

coach  or  boat  is  in  danger  of  oversetting  ?     7.  On  what  principle  do  ^ 

we  regulate  our  ordinary  actions  ?     8.  Show  by  fig.  12.  the  comrnon  ^ 

centre  of  gravity  of  two  bodies.    9.  Illustrate  by  fig.  4.  the  overturning  ; 
of  a  body,  when  the  line  of  direction  falls  out  of  the  base. 


THE   LAWS   OP  MOTION. 


LESSON  18. 

The  Laws  of  Motion. 

Momen'tum,  (pi.  momenta)  the  force  acquired  by  different  masses 
of  matter  moving  with  different  velocities.  A  body,  twice  the 
weight  of  another,  moving  with  equal  velocity,  will  strike  with 
twice  the  momentum, — with  twice  the  velocity,  with /owr  times 
the  momentum, — with  three  times  the  velocity,  with  six  times 
the  momentum,  and  so  on. 

A  BODY  is  in  motion  whenever  it  is  changing  its  situation 
with  regard  to  a  fixed  point,  and  the  cause  which  produces  mo- 
tion is  called/orc6.  The  causes  of  motion,  or  the  motive  powers 
are  either  muscular,  as  the  action  of  men  and  other  animals, 
or  mechanical,  as  the  force  of  wind,  water,  gravity,  the  pres- 
sure of  the  atmosphere  or  any  elastic  medium,  and  steam. 
The  motion  of  a  body  acted  upon  by  a  single  force  is  always 
in  a  straight  line,  in  the  direction  in  which  it  received  the 
impulse;  and  the  degree  of  quickness  with  which  it  moves, 
or  the  velocity,  must  be  proportional  to  the  force  by  which 
it  is  impelled.  If  a  given  force,  therefore,  will  produce  a 
given  motion,  a  double  force  will  produce  the  double  of  that 
motion.  If  a  new  force  be  impressed  upon  a  body  in  motion, 
its  motion  will  be  increased  proportionably  to  the  new  force 
impressed.  The  velocity  with  which  a  body  moves  is  mea- 
sured by  the  space  passed  over,  divided  by  the  time  which  it 
employs  in  that  motion  ;  for  if  you  travel  one  hundred  miles 
in  twenty  hours,  your  velocity  is  five  miles  in  each  hour. 
You  may  reverse  this  rule  and  say,  that  the  time  is  equal  to 
the  space  divided  by  the  velocity,  for  one  hundred  divided 
by  five  gives  twenty  hours  for  the  time  ;  and  you  may  say 
also  that  the  space  is  equal  to  the  velocity  multiplied  by  the 
time,  for  twenty  multiplied  by  five  gives  one  hundred  miles 
for  the  space. 

Motion  is  uniform,  accelerated,  or  retarded.  Uniform 
motion  is  regular,  and  at  an  equal  rate  throughout.  The 
hand  of  a  watch  is  an  example  of  uniform  motion,  for  it 
passes  over  equal  spaces  in  equal  times.  If  neither  gravity 
nor  any  other  force  opposed  its  motion,  a  ball  thrown  by  the 
hand  would  proceed  onwards  in  a  right  line,  and  with  a  uni- 
form velocity  for  ever.  Perpetual  motion,  however,  cannot 
be  produced  by  art,  for  gravity  ultimately  destroys  all  motion 


I 

36  THE    LAWS    OP   MOTION.  i 

that  human  powers  can  produce.  Accelerated  motion  takes  j 
place,  when  the  motive  power  continues  to  act  upon  any  1 
body,  so  that  its  motion  is  continually  increased.  When  a 
stone  falls  from  a  height,  the  impulse  which  it  receives  from  j 
gravity  during  the  first  instant  of  its  fall,  would  be  sufficient  ^ 
to  bring  it  to  the  ground  with  a  uniform  velocity ;  but  the 
stone  is  not  acted  upon  by  gravity  merely  at  the  first  instant  \ 
of  its  fall, — this  power  continues  to  impel  it  during  the  whole  1 
of  its  descent,  and  it  is  this  continued  impulse  which  acce-  | 
Jerates  its  motion.  It  has  been  found  by  experiment  that  \ 
heavy  bodies,  descending  from  a  height  by  the  force  of  gra-  ; 
vity,  fall  sixteen  feet  the  first  second  of  time,  three  times  that  ; 
distance  in  the  next,  five  times  in  the  third  second,  seven  J 
times  in  the  fourth,  and  so  on,  regularly  increasing  their  ve- 
locities according  to  the  number  of  seconds  during  which  i 
ihe  body  has  been  falling.  Retarded  motion  is  that  of  a  : 
))ody  which  moves  every  moment  slower  and  slower ;  and  it  J 
{3  produced  by  some  force  acting  upon  a  body  in  a  direction  ,i 
Opposite  to  that  which  first  put  it  in  motion,  as  when  a  stone  \ 
IS  thrown  upwards,  its  velocity  is  gradually  diminished  by  ] 
(he  power  of  gravity.  ^ 

The  force,  or  power,  with  which  a  body  in  motion  strikes  i 
against  another  body,  is  called  its  momentum.  It  is  composed  * 
^f  its  quantity  of  matter,  multiplied  by  its  quantity  of  motion  ;  { 
or  in  other  words,  its  weight  and  its  velocity.  A  small  body  i 
may  have  a  greater  momentum  than  a  large  one,  provided  its  : 
velocity  be  sufficiently  greater ;  the  momentum  of  an  arrow  j 
l?hot  from  a  bow,  for  instance,  must  be  greater  than  a  stone 
thrown  by  the  hand.  The  momentum  of  bodies  is  one  of  j 
the  most  important  points  in  mechanics ;  for  you  will  find,  | 
that  it  is  from  opposing  motion  to  matter,  that  machines  de-  \ 
rive  their  powers.  i 

When  a  body  in  motion  strikes  against  another  body,  it  ■ 
meets  with  resistance  from  it ;  and  the  resistance  of  the  body  • 
tt  rest  will  be  equal  to  the  blow  struck  by  the  body  in  mo-  \ 
^ion  ;  or  to  express  the  same  in  philosophical  language,  action  \ 
4nd  re-action  will  be  equal  and  in  opposite  directions.  It 
Appears,  therefore,  that  one  body  acting  upon  another,  loses  1 
as  much  motion  as  it  communicates,  and  that  the  sum  of  th«  \ 
Motions  of  any  two  bodies  in  the  same  line  of  direction,  can-  ; 
"ot  be  changed  by  their  mutual  action.  From  the  action  \ 
*M&  re-action  of  bodies  we  may  learn  in  what  manner  a  bird,  j 


iCOMPOUND    MOTION.  37 

by  the  stroke  of  its  wings,  is  able  to  support  its  weight  in  the 
air.  If  the  force  with  which  it  strikes  the  air  below  it,  is 
equal  to  the  weight  of  its  body,  then  the  re-action  of  the  air^ 
upwards  is  likewise  equal  to  it,  and  the  bird  being  acted 
upon  by  two  equal  forces  in  contrary  directions,  will  rest  be- 
tween them.  If  the  force  of  the  stroke  is  greater  than  its 
weight,  the  bird  will  rise  with  the  difference  of  these  two 
forces  ;  and  if  the  stroke  be  less  than  its  weight,  then  it  will 
sink  with  the  difference.  In  the  act  of  rowing,  the  water  is 
struck  with  the  oars,  in  a  direction  opposite  to  that  in  which 
the  boat  is  required  to  move ;  and  the  boat,  is  driven  along 
by  the  reaction  of  the  water  on  the  oars. 

Questions. — 1.  When  is  a  body  in  motion  ?  2.  What  is  force  ? 
3.  What  are  the  motive  powers  ?  4.  In  what  direction  is  the  motion 
of  a  body  acted  upon  by  a  single  force  ?  5.  What  is  velocity  ?  6.  To 
what  is  the  velocity  of  a  moving  body  proportioned  ?  7.  How  do  you 
calculate  the  velocity  of  a  moving  body  ?  8.  What  is  uniform  motion  ? 
9.  Accelerated?  10.  Retarded.''  11.  Why  cannot  perpetual  motion 
be  produced  by  art  ?  12.  When  a  stone  falls  from  a  height,  how  does^ 
gravity  accelerate  its  motion .'  13.  What  is  said  of  the  distances 
through  which  heavy  bodies  fall  in  successive  seconds  of  tim*  ?  14. 
What  is  an  instance  of  retarded  motion  .''  15.  What  is  the  momentum 
of  a  body.'  16.  Of  what  composed.''  17.  Why  is  it  so  important 
with  respect  to  mechanics  ?  18.  Wliat  is  meant  by  the  term  reaction  ? 
19.  To  what  is  reaction  equal  ?  20 .  Explain  the  manner  in  which 
birds  support  themselves  in  the  air. 


LESSON  19. 

Compound  Motion. 

Projec'tile,  impelled  forward  in  a  right  line. 
Horizon'tal,  parallel  to  the  horizon,  on  a  level. 
Oblique',  not  direct,  not  perpendicular,  not  parallel. 

If  a  body  be  struck  by  two  equal  forces  in  opposite  direc- 
tions, it  will  not  move  at  all ;  but  if  the  forces,  instead  of 
acting  on  the  body  in  opposition,  strike  it  in  two  directions 
inclined  to  each  other,  it  will  follow  the  direction  of  neither 
of  the  forces,  but  will  move  in  a  line  between  them.  There 
are  many  instances  in  nature,  of  motion  produced  by  several 
powers  acting  at  the  same  time.  If  a  ship  at  sea  sail  before 
the  wind  directly  east,  and  a  current  set  from  the  north,  it 
will  be  driven  in  a  direction  between  the  south  and  east. 
4 


38  COMPOUND    MOTION. 

A  ball  fired  from  a  cannon  is  acted  upon  by  two  forces,  the 
one  is  that  occasioned  by  the  powder,  the  other  is  the  force 
of  gravity. 

Circular  motion  is  the  result  of  two  forces  on  a  body,  by 
one  of  which  it  is  projected  forward  in  a  right  line,  whilst 
by  the  other  it  is  confined  to  a  fixed  point.  When  you 
whirl  a  ball,  for  instance,  which  is  fastened  to  your  hand 
with  a  string,  the  ball  moves  in  a  circular  direction  ;  be- 
cause it  is  acted  upon  by  two  forces,  that  given  it  by  your- 
self, which  represents  the  force  of  projection,  and  that  of  the 
string  which  confines  it  to  your  hand.  If  during  its  motion 
the  string  were  suddenly  to  break,  the  ball  would  fly  off  in  a 
straight  line ;  being  released  from  confinement  to  the  fixed 
point,  it  would  be  acted  on  but  by  one  force,  and  motion 
produced  by  one  force  is  always  in  a  right  line.  The  force 
which  confines  a  body  to  a  centre  round  which  it  moves,  is 
called  the  centripetal  force  ;  and  that  force  which  impels  a 
body  to  fly  from  the  centre,  is  called  the  centrifugal  force. 
In  circular  motion  these  two  forces  constantly  balance  each 
other,  otherwise  the  revolving  body  would  either  approach 
the  centre,  or  recede  from  it,  according  as  the  one  or  the 
other  prevailed.  If  any  cause  should  destroy  the  centripetal 
force,  the  centrifugal  force  would  alone  impel  the  body,  and 
it  would  fly  off  in  a  right  line  in  the  direction  in  which  it 
was  moving,  at  the  instant  of  its  release.  When  a  stone, 
whirled  round  in  a  sling,  gets  loose,  it  flies  off  in  a  right  linCj 
called  a  tangent,  because  it  touches  the  circumference  of  the 
circle  in  which  the  stone  was  revolving. 

It  is  by  the  laws  of  circular  motion  that  the  moon  and  all 
the  planets  revolve  in  their  orbits.  The  moon,  for  instance, 
has  a  constant  tendency  to  the  earth,  by  the  attraction  of 
gravitation,  and  it  lias  also  a  tendency  to  proceed  in  a  right 
line,  by  that  projectile  force  impressed  upon  it  by  the  Crea- 
tor ;  now,  by  the  joint  action  of  these  two  forces  it  describes 
a  circular  motion.  If  the  projectile  force  were  to  cease, 
the  moon  must  fall  to  the  earth  ;  and  if  the  force  of  gravity 
were  to  cease  acting  upon  the  moon,  it  would  fly  off  into 
infinite  space. 

When  you  throw  a  ball  in  a  horizontal  or  oblique  direc- 
tion, it  describes  a  curve  line  in  falling,  and  is  acted  upon 
by  three  forces ;  the  force  of  projection,  which  you  commu- 
nicated to  it ;  the  resistance  of  the  air,  which  diminishes  its 


THE    PENDULUM.  39 

velocity,  virithout  changing  its  direction ;  and  the  force  of 
gravity,  which  finally  brings  it  to  the  ground.  The  curve  line 
which  the  ball  describes  is  called  in  geometry  aparab'ola. 

A  pendulum  consists  of  a  line,  or  rod,  to  one  end  of  which 
a  weight  is  attached,  and  it  is  suspended  by  the  other  to  a 
fixed  point,  about  which  it  is  made  to  vibrate.  Without 
being  put  in  motion,  a  pendulum,  like  a  plumb  line,  hangs 
perpendicularly  to  the  general  surface  of  the  earth,  by  which 
it  is  attracted ;  but  if  you  raise  a  pendulum,  gravity  will 
bring  it  back  to  its  perpendicular  position.  It  will,  how- 
ever, not  remain  stationary  there,  for  the  velocity  it  has  re- 
ceived during  its  descent  will  impel  it  onwards,  and  it  will 
rise  on  the  opposite  side  to  an  equal  height ;  from  thence  it 
is  brought  back  by  its  gravity,  and  again  driven  by  the  im- 
pulse of  its  velocity.  Were  it  possible  to  remove  the  ob- 
stacles occasioned  by  the  resistance  of  the  air,  and  by  the 
friction  of  the  part  by  which  it  is  suspended,  the  motion  of 
a  pendulum  would  be  perpetual,  and  its  vibrations  perfectly 
regular ;  being  of  equal  distances,  and  performed  in  equal 
times.  The  metallic  rods  of  pendulums  are  expanded  by 
heat  and  contracted  by  cold  ;  clocks  therefore  will  go  faster 
in  winter,  and  slower  in  summer,  for  the  longer  a  pendulum 
is,  the  slower  are  its  vibrations.  The  common  remedy  for 
this  inconvenience  is  raising  or  lowering  the  weight  of  the 
pendulum,  by  means  of  a  screw,  as  occasion  may  require. 
Pendulums  vibrate  faster  towards  the  poles,  and  slowest  at 
the  equator.  This  is  accounted  for  by  the  earth's  diameter 
being  greater  through  the  equator  than  through  the  poles. 
All  bodies  on  the  earth's  surface  are  drawn  to  its  centre  by 
the  force  of  gravity ;  and  more  powerfully  as  the  square  of 
their  distance  is  less.  Hence,  if  one  portion  of  the  earth's 
surface  be  farther  from  its  centre  than  another,  the  force  of 
gravity  on  a  pendulum  in  one  place  must  be  less  than  in 
another  ;  and  consequently  the  pendulum  will  vibrate  slower 
or  faster  according  to  its  situation.  And  this  is  found  to  be 
actually  the  case. 

It  was  from  observing  the  difference  in  the  vibrations  of 
pendulums  of  the  same  length,  that  the  difference  of  gravity 
was  discovered,  and  the  true  figure  of  the  earth  ascer- 
tained. Pendulums  vibrating  seconds,  at  London,  are 
thirty-nine  inches  and  two-tenths  in  length ;  but  at  the  equa- 
tor  about  thirty-nine   inches   and  one-tenth.     Pendulums 


40  MECHANICAL   POWERS. 

of  the  same  length  vibrate  in  the  same  time  however  differ* 
ent  in  weight. 

Questions. — 1.  In  what  direction  will  a  body  move  when  impel- 
led by  two  forces  ?  2.  Describe  the  motion  of  a  ship  as  impelled  by 
the  wind  and  a  current.  3.  What  is  circular  motion?  4.  The  ex- 
ample ?  5.  Centripetal  force  ?  6.  Centrifugal  ?  7.  What  is  said  of 
these  two  forces  ?  8.  What  is  a  tangent  ?  9.  What  is  said  of  the 
motion  of  the  moon?  10.  What  is  a  parabola  ?  11.  A  pendulum? 
12.  Describe  the  manner  in  which  a  pendulum  .vibrates.  13.  Why  ia 
not  the  motion  of  a  pendulum  perj)etual  ?  14.  Why  do  clocks  go 
faster  in  winter  than  in  summer  ?  15.  Why  do  pendulums  vibrate 
faster  towards  the  poles  than  at  the  equator  ? 

Note.  Tlie  centrifugal  force  is  stronger  at  the  equator  than  at  the 
poles  J  and  as  it  tends  to  drive  bodies  from  the  centre,  it  is  necessarily 
opposed  to,  and  must  lessen  the  power  of  gravity,  which  attracts  them 
towards  the  centre.  The  equatorial  diameter  of  the  earth  is  stated 
by  some  to  be  34  miles,  and  by  others  to  be  26  miles  longer  than  the 
polar  diameter.  IG.  Illustrate  by  figure  1.  the  composition  and  re- 
solution of  motion. 


LESSON  20. 

Mechanical  Powers. 

Centre  of  motion  is  that  point  which  remains  at  rest   wliile  all 

the  other  parts  of  a  body  move  round  it. 
Axis  of  motion  is  the  line  about  which  a  revolving  body  moves. 
Equilib'rium,  equipoise,  equality  of  weight. 

The  mechanical  powers  are  simple  instruments  or  ma- 
chines in  the  hands  of  man,  by  which  he  is  enabled  to  raise 
great  weights,  and  overcome  such  resistances  as  his  natural 
strength  could  never  effect  without  them.  They  are  six  in 
number,  the  lever,  the  pulley,  the  wheel  and  axle,  the  in- 
clined plane,  the  wedge,  and  the  screw,  one  or  more  of  which 
enters  into  the  composition  of  every  machine.  In  order  to 
understand  the  power  of  a  machine,  four  things  are  to  be 
considered  ;  the  power  that  acts,  which  consists  in  the  effort 
of  men  or  horses,  of  weights,  springs,  running  waters,  wind, 
and  steam ;  the  resistance  which  is  to  be  overcome  by  the 
power,  which  is  generally  a  weight  to  be  moved  ;  the  centre 
of  motion,  or,  as  it  is  termed  in  mechanics,  the  fulcrum,  which 
is  the  point  about  which  all  the  parts  of  a  body  move  ;  and 
lastly,  the  respective  velocities  of  the  power,  and  of  the  re- 
sistance, which  must  depend  upon  their  respective  distances 


THE    LEVER.  41 

from  the  axis  of  motion.  The  power  and  weight  are  said  to 
balance  each  other,  or  to  be  in  equilibrium,  when  the  effort 
of  the  one  to  produce  motion  in  one  direction,  is  equal  to 
the  effort  of  the  other  to  produce  it  in  the  opposite  direction. 
The  power  of  a  machine  is  calculated,  when  it  is  in  a  state 
of  equilibrium,  that  is,  when  the  power  just  balances  the  re- 
sistance opposed,  and  the  momentum  of  each  is  equal. 

The  lever  is  any  inflexible  bar  of  iron,  wood,  or  other  ma- 
terial, which  serves  to  raise  weights,  while  it  is  supported  at 
a  point  by  a  prop  or  fulcrum,  on  which,  as  the  centre  of  mo- 
tion, all  the  other  parts  turn.  There  are  three  different  kinds 
of  levers.  The  Jirst  kind  has  the  fulcrum  between  the 
weight  and  the  power,  as  in  steelyards  and  scissors.  It  is 
the  most  common  kind,  and   is  chiefly  used  ror  loosening 

rge  ijj^ks  ;  or  for  raising  great  weights  to  small  heights, 
orderto  place  ropes  under  them.     Let  it  be  required  to 

aise  a  body  which  weighs  ten  hundred  pounds,  by  the 
^trength  of  a  man  equal  to  a  hundred  pounds  weight.  Now 
asNthe  man's  strength  is  only  equal  to  the  tenth  part  of  the 
weight  of  the  body  to  be  raised,  the  arm  of  the  lever,  to 
which  his  strength  id  to  be  applied,  must  be  ten  times  as 
long  as  the  other,  in  order  that  the  power  and  weight  may 
be  in  equilibrium"..  A  balance  is  a  lever  of  this  kind,  with 
equal  arms ;  but  if  one  arm  be  four  times  the  length  of  the 
other,  then  it  is  a  lever  which  gains  power  in  the  proportion 
of  four  to  one,  and  a  single  pound  weight,  put  into  the  scale 
which  is  suspended  from  the  long  arm,  will  balance  four 
poflnds  in  the  other.  The  second  kind  of  lever  is  when  the 
prop  is  at  one  end,  the  power  at  the  other,  and  the  weight 
between  them.  It  explains  why  two  men  carrying  a  burden 
upon  a  pole,  may  bear  unequal  shares  according  to  their 
strength,  by  placing  it  nearer  to  the  one  than  the  other.  He, 
to  whom  the  burden  is  five  times  the  nearest,  will  have  to 
bear  five  times  as  much  weight  as  the  other.  In  the  case 
of  two  horses  of  unequal  strength  the  beam  may  be  so  di- 
vided, that  they  shall  draw  in  proportion  to  their  respective 
ability.  The  third  kind  of  lever  is  when  the  prop  is  at  one 
end,  the  weight  at  the  other,  and  the  power  applied  between 
them.  To  this  kind  are  generally  referred  the  bones  of  a 
man's  arm,  for  when  he  lifts  a  weight  by  the  hand,  the  mus- 
cle that  exerts  its  force  to  raise  that  weight,  is  fixed  to  the 
bone  about  one-tenth  part  as  far  below  the  elbow  as  the  hand 
4* 


43  THE    PULLEY. 

is.  The  elbow  being  the  centre  round  which  the  lower  part 
of  the  arm  turns,  the  muscle,  therefore,  must  exert  a  force 
ten  times  as  great  as  the  weight  to  be  raised.  At  first  view 
this  may  appear  a  disadvantage,  but  the  loss  of  power  is  com- 
pensated by  the  gain  of  velocity,  and  by  the  beauty  and  com- 
pactness of  the  limb. 

Questions. — 1.  What  are  raechauical  powers?  2.  What  four 
things  are  necessary  to  be  considered  in  order  to  understand  the  pow- 
er of  a  n>achine  ?  3.  When  do  the  power  and  w^ght  balance  each 
other  ?  4.  Wljat  is  a  lever  ?  3.  Describe  the  lever  oTthe  first  kind.  6. 
What  are  some  instances  of  it,  and  to  what  purposes  are  they  applica- 
ble ?  7.  What  is  said  of  a  bala|)ice  ?  8.  Describe  the  second  kind  of 
4evcr.  9.  What  does  it  explainr*?  JO.  What  is  the  third  kind  of  lever  .' 
H.  Show  ho'^v^^e  bones  of  a  maaPs  arm  make  a  lever  of  this  kind. 
12.  How  is  thJfcoss  of  power  compensated  ?  ^3.  Give  an  illustration 
by  fig.  7.  of  the  first  kind  of  lever.  14.  Of  the  secondkind,  bvfigure 
9  and  5.     15.  Of  the  third  kind)  hgr  figures  10  and  2.      .^       #^'      - 


i 


The  Pulley,  Wheel  cQm  Axle,  anarWnclined  Plane 


The  pulley  is  formed  by  a  sniall  wheel,  t^%/^  of  wood  or 
metal,  with  a  groove  in  its  circumference,  which  is  placed  in 
a  frame  and  turns  on  an  axis.  The  wheel  is  usually  called 
a  sheeve,  and  is  so  fixed  in  the  frame,  or  block,  as  to  move 
round  a  pin  passing  through  its  centre.  Pullies  are  of  two 
kinds  ;  Jixed,  which  do  not  move  out  of  their  places ;  atid 
moveable,  which  rise  and  fall  with  the  weight.  A  single  fixed 
pulley  gives  no  mechanical  advantage,  but  it  is  of  great  im- 
portance in  changing  the  direction  of  power,  and  is  much 
used  in  buildings  for  drawing  up  small  weights,  for  a  man 
may  raise  a  weight  to  any  height  without  the  fatigue  of  as- 
cending a  ladder.  In  the  single  moveable  pulley,  the  advan- 
tage gained  is  as  two  to  one  ;  that  is,  a  power  exerted  by  the 
hand  of  ten  pounds  will  balance  a  weight  of  twenty  pounds. 
In  a  system  of  pullies,  the  power  gained  nmst  be  estimated, 
by  doubling  the  number  of  pullies  in  the  lower  or  moveable 
block.  So  that  when  the  fixed  block  contains  two  pullies 
which  only  turn  on  their  axes,  and  the  lower  block  also  con- 
tains two,  which  not  only  turn  on  tlieir  axes,  but  rise  with 
the  weight,  the  advantage  gained  is  as  four  to  one.     In  an 


THE    INCLINED    PLANE.  4S| 

eKftnple  of  this  kind,  you  will  perceive,  that  by  raising  the 
weight  an  inch,  there  are  four  ropes  shortened  each  an  inch, 
and  therefore  the  hand  must  have  passed  through  four  inches 
of  space  in  raising  the  weight  a  single  inch  ;  which  esta- 
blishes the  maxim,  that  what  is  gained  in  power  is  lost  in 
space. 

The  next  mechanical  power  is  the  wheel  and  axle,  which 
consists  of  a  cylinder,  and  a  wheel  fastened  to  it,  or  of  a  cy- 
linder with  projecting  spokes.     The  power  being  applied  at 
the   circumference  of  the   wheel,  the  weight  to  be  raised  is 
fastened  to  a  rope  that  coils  round  the  axle.     The  advantage 
gained  is  in  proportion  as  the  diameter  of  the  wheel  exceeds 
that  of  the  axle,     Svmpose  a  wheel  to  be  twelve  feet  diame- 
ter, and  the  axle  one  K>ot^  the  power  acting  at  the  circumfe- 
rence oFthe  wheel  moves  over  twelve  times  the  space  which 
the  circlnifercnce  of  the  axle  dbes,   'Hence,  twelve  hundred 
weight  may  be  raised  with  the  power  of  one  hundred  weight. 
The  wheel  and  axle  maj^e  considered  as  a  perpetual  lever, 
the  centre  of  the  axle  being" the  fulcrum,  half  the  diameter 
of  the  wbeel  th€  long  arjm,  and  half  the  diameter  of  the  axle 
the  shor^m.     Nowj'^frbm  this  it  is  evident,  that  the  greater 
the  diarifeter  of  the  wheel,  and  the  smaller  the  diameter  of 
the  axle,  the  stroller  is  the  power  of  this  machine  ;  but  then 
the  weight  mu^  rise  slower  in  proportion.     A  useful  appli- 
cation of  the  wheel  and  axle  is  the  Cran@.  used  on^harfsfor . 
drawing  goods  up  from  a  ship.     A  man  sets  a  great  wh©^ 
in  motion  by  pressing  on  the  spokes  at  the  rim,  and  the  rope   . 
to  which  the  goods  are  attached  is  wound  round  the  axl^ 
The  wheel  is  sometimes  put  in  motion  by  a  man  in  4he   imF 
side,  who  is  in  an  upright  position,  and  keeps  walking  on  tlio 
bars,  as  if  ascending  stairs,  wh^eh  keeps  the  wheel  revolving. 

The  inclined  plane  is  nothing  more  than  a  slope,  or  de- 
clivity, frequently  used  to  facilitate  the  drawing  up  of  weight?. 
The  increase  of  the  power  is  in  the  proportion  of  the  length 
of  the  plane  to  its  height ;  that  is,  the  more  the  plane  is 
lengthened,  or  its  height  shortened,  the  less  is  the  resistance 
to  be  overcome.  If  a  plane  be  twenty  feet  long,  and  the 
perpendicular  height  be  four  feet,  or  one-fifth  of  the  length, 
then  five  hundred  pounds  would  be  balanced  on  it  by  one 
hundred,  because  the  plane  is  five  times  the  length  of  the 
perpendicular  height  to  which  the  weight  is  to  be  raised.  If 
the  height  be  two  feet,  or  one-tenth  of  the  length,  then  fifty 


44  THE    WEDGE    AND    SCREW. 

pounds  will  balance  the  five  hundred.  It  is  much  less  labori- 
ous to  ascend  a  hill  by  a  winding  gentle  ascent  than  to  climb 
up  a  steep  declivity.  In  addition  to  there  being  a  greater 
force  required  in  ascending  a  hill,  horses,  that  draw  a  load, 
are  placed  in  a  position  in  which  they  can  exert  but  a  small 
part  of  their  usual  strength.  The  principle  of  the  inclined 
plane  is  applied  to  the  construction  of  carriage-ways,  for  the 
conveyance  of  heavy  loads  up  steep  elevations.  It  is  applied 
also  in  rail-ways,  the  use  of  which  has  been  hitherto  confined, 
almost  exclusively,  to  coal-works,  and  other  mines.  Inven- 
tions, whose  only  recommendations  are  simplicity  and  use- 
fulness, are  often  suffered  to  lie  long  in  a  state  of  public  neg- 
lect, while  others  of  more  imposing  asjjj^ct  are  readily  adopt- 
ed.    It   has  been  remarked  with   respect  to  Great  Britain 


that  the  time  has  at  length  arrived,  when  carriage3|||taffin^  J 

on  level  surfaces,  or  on  gently   inclining  planes,  ^^||IBp^ttJ|^  "ij 

friction,  and  without  obstructions,  are  fast  spreading  over  j 

the  face  of  the  country.              ^,  t  i 

Questions. — 1.  How  is  the  pulley  farmed  ?    S*;  What  are  the  two 

kinds  of  pullies  ?     3.  What  is  said  of  the  siSfj^  fixed  pulley  ?     4.  What  ' 

advantage  is   gained   in   a  single  moveable^  jiulley  ?     5.  How  is  the  i 

power  gained  to  be  estimated  in  a  system  of  pullies  ?     G.  How  is  this  ■ 

explained  and  what  maxim  does  it  establish  ?     "^U^escvibe  the  wheel  i 

and  axle.     8.  In  what  proportion  is  advantage  ^nncd  in  this  mecha-  ' 

nical  power  ?     J).  What   is  the   example  ?     10.  Why  may  the  wheel  i 

and  axle  ba|:onsidered  as  a  perpetual  lever  ?     11.  What  application  is  | 

made  of  this  power  ?     12.  What  is  an  inclined  plane  ?     13.  In  what  .^ 

proportion  is  the  increase  of  power  .?     14.  What  is   the  example   for  ; 

illustrating  this  ?     15.  What  application  is  made  of  the  principle  of  ] 

{{lo  inclined  plane  ?     IG.  What  has  been  remarked  concerning  the  use  ; 

of  rail-ways  ?     17.  With  respect  to  Great  Britain  ?     iS.  Explain  the  g 

single   moveable  pulley  by  fig.  13. — system  of  pullies  by  fig.  15.     19.  ^ 

Illustrate  the  power  of  the  whe^  and  axle  by  fig.  11.    20.  Inclined  ^ 
plane  by  fig.  8. 


LESSON  22..  I 

The  Wedge  and  Screw.       .  -l 

Percus'sion,  the  impression  a  body  makes  in  falling  or  striking 

upon  another,  or  the  shock  of  two  bodies  in  motion.  ^ 

Sili'ceous,  flinty  ;  see  Lesson  63.  ^ 

The  wedge  may  be  considered  as  two  equally  inclined  i 
planes  united  at  their  bases.    The  advantage  gained  by  it  i«  * 


THE    SCREW. 


4^ 


in  the  proportion  of  the  slant  side  to  half  the  thickness  of 
the  back ;  so  that  if  the  back  of  a  wedge  be  two  inches 
thick,  and  the  side  twenty  inches  long,  any  weight  pressing 
on  the  back  will  balance  twenty  times  as  much  acting  ok 
the  sides.  But  the  great  use  of  a  wedge  lies  in  its  bein^- 
urged,  not  by  pressure,  but  usually  by  percussion,  as  by  the 
blow  of  a  hammer  or  mallet;  for  the  momentum  of  the  blow 
is  greater,  beyond  comparison,  than  the  application  of  any 
dead  weight,  or  pressure,  such  as  is  employed  in  the  other 
mechanical  powers.  Hence  it  is  used  in  splitting  wood 
and  rocks,  and  even  a  large  ship  may  be  raised  to  a  small 
height  by  driving  a  wedge  below  it.  As  all  instruments, 
which  slope  off  to  an  edge  on  one  side  only,  may  be  ex-' 
plained  by  the  principle  of  the  inclined  plane ;  so  those  that 
decline  to  an  edge  on  both  sides,  may  be  referred  to  the  prin- 
ciple of  the  wedge.  A  saw  is  a  series  of  wedges,  on  which 
the  motion  is  oblique  to  the  resistance.  A  knife  cuts  best 
when  it  is  drawn  across  the  substance  which  it  is  to  divide  ; 
and  the  reason  is,  that  the  edge  of  a  knife  is  In  reality  a  very 
fine  saw,  and  therefore  acts  best  when  used  like  that  instru- 
ment. It  is  usual  in  separating  large  mill-stones  from  the 
siliceous  sand-rocks,  in  some  parts  of  Derbyshire,  in  Eng- 
land, to  bore  horizontal  holes  under  them  in  a  circle,  and 
fill  these  with  wedges  made  of  dry  wood,  which  gradually 
swell  as  they  imbibe  moisture,  and  in  a  day  or  two  lift  up 
the  mill-stone  without  breaking  it. 

The  last  mechanical  power  is  the  screw,  which  is  a  kind 
of  perpetual  inclined  plane,  the  power  of  which  is  still  farther 
assisted  by  the  addition  of  a  handle  or  lever,  where  the  power 
acts ;  so  that  the  advantage  gained  is  in  proportion  as  the 
circumference  of  the  circle,  made  by  the  handle  or  lever,  is 
greater  than  the  distance  between  thread  and  thread  in  the 
screw.  The  screw  may  be  conceived  to  be  made  by  cutting 
a  piece  of  paper  into  the  form  of  an  inclined  plane,  and 
then  wrapping  it  round  a  cylinder.  The  edge  of  the  paper 
will  form  a  spiral  line  round  the  cylinder,  which  will  answer 
to  the  thread  of  the  screw.  With  the  addition  of  the  lever, 
the  screw  forms  a  very  powerful  machine,  employed  either 
for  compressions,  or  to  raise  heavy  weights.  It  is  used  by 
book-binders  to  press  the  leaves  of  books  together ;  and  is  the 
principal  machine  used  for  coining  money ;  for  taking  off 
copper-plate  prints ;  and  for  printing  in  general. 


46  THE  SCREW. 

All  machines  are  composed  of  one  or  more  of  the  six  mc-^j 
chanical  powers  which  we  have  examined.  Their  force  isl 
diminished  in  a  considerable  degree  by  friction,  by  which  is  ] 
meant  the  resistance  with  which  bodies  meet  in  rubbing  i 
against  each  other.  There  is  no  such  thing  as  perfect  smooth-  i 
ness  or  evenness  in  nature :  polished  metals,  though  they  I 
wear  that  appearance  more  than  any  other  bodies,  are  far  \ 
from  possessing  it  in  reality,  and  through  a  good  magnifying-  ^ 
glass  their  inequalities  may  frequently  be  perceived.  When  j 
the  surfaces  of  two  bodies,  therefore,  come  into  contact,  the  \ 
prominent  parts  of  the  one  will  often  fall  into  tlie  hollow  ^ 
parts  of  the  other,  and  occasion  more  or  less  resistance  to  1 
motion.  Friction  is  usually  computed  to  destroy  one  third  ' 
of  the  power  of  the  machine.  The  application  of  oil  lessens  i 
friction,  because  it  acts  as  a  polish  by  filling  up  th&"  cavitiesi 
of  the  rubbing  surfaces,  and  thus  making  them  slide  over  \ 
each  other  the  more  easily.  There  are  two  kinds  of  friction,  l| 
the  one  occasioned  by  the  sliding  of  the  flat  surface  of  a  body, '] 
and  the  other  by  the  rolling  of  a  circular  body.  The  re-  : 
sistance  resulting  from  the  first  is  much  the  most  considera-  ] 
ble;  whilst  in  the  latter  the  rough  parts  roll  over  each  other  | 
with  comparative  facility ;  hence  it  is  that  wheels  are  often  \ 
used  for  the  sole  purpose  of  diminishing  the  resistance  of  < 
friction.  The  power  of  a  machine  is  considerably  affected  j 
by  the  resistance  of  the  air.  ] 

In  all  machines  what  is  gained  in  power  is  lost  in  time.  If  ; 
a  man  can  raise,  fty  a  single  fixed  pulley,  a  beam  to  the  top  \ 
of  a  house  in  two  minutes,  he  will  be  able  to  raise  six  such  ; 
beams  in  twelve  minutes;  but  with  six  pullies,  the  three  | 
lower  ones  being  moveable,  he  will  raise  six  beams  with  the  '• 
same  ease  at  once  ;  but  he  will  be  six  times  as  long  about  it, 
that  is,  twelve  minutes,  because  his  hand  will  have  six  times  j 
as  much  space  to  pass  over.  One  capital  advantage  in  the 
mechanical  powers  is,  that  if  the  six  beams  were  in  9ne  '\ 
piece,  it  might  be  raised  at  once,  though  it  would  be  impos-  j 
sible  to  move  it  by  the  unassisted  strength  of  a  single  man.      ! 

Questions. — 1.  What  is  the  wedge  ?     2.  The  advantage  gained  ; 

by  it .''     3.  In  what  does  its  great  use  lie  ?     4.  What  is  said  of  inslru-  ■ 

ments  ?   5.  A  saw  ?     G.  A  knife  ?     7.  How  are  mill-stones  obtained  in  | 

Derbyshire  ?     7.  What   is  the  screw  ?     8.  What  is    the    advantage  i 

fained  by  it  ?     9.  How  may  the  screw  be  conceived  to  be  made  ?     10.  ^ 
or  what  uses  is  it  employed .''     11.  What  is  friction  1     12.  What  part 

of  a  machine's  power  does  friction  destroy.'    [Note.  If  60  pounds  « 


LAWS  OF  FLUIDS.  47 

are  required  to  balance  any  weight  with  a  mechanical  power,  80 
pounds  will  be  wanted  to  put  the  machine  in  motion.]  13.  How  does 
oil  lessen  friction.?  14.  What  are  the  two  kinds  of  friction?  15. 
How  does  it  appear  that  in  the  pulley  what  is  gained  in  power  is  lost 
in  time  ?  16.  Explain  the  principle  of  the  wedge  by  fig.  6.  17.  Of 
the  screw  by  fig.  3. 


LESSON  23. 

TJie  Lmos  of  Fluids. 

Hydrostat'ics,  a  term  formed  of  two  Greek  words,  which  signify 
water,  and  the  science  which  considers  the  weight  of  bodies, 
viz.  statics. 

Gas,  all  kinds  of  air  differing  from  the  atmosphere  are  called  gas. 

Cu'bical,  having  six  square  and  equal  sides. 

Or'ifice,  any  opening  or  perforation. 

A  FLUID  is  a  body,  the  parts  of  which  yield  to  any  impres- 
sion, and  are  easily  moved  among  each  other.  Philosophers 
have  generally  imagined  that  the  particles  of  which  fluids 
are  composed  must  be  exceedingly  small,  because  with  their 
best  glasses,  they  have  never  been  able  to  discern  them. 
And  they  contend  that  these  particles  must  be  round  and 
smooth,  since  they  are  so  easily  moved  among  one  another. 
This  supposition  will  account  for  many  circumstances  which 
belong  to  them.  If  they  are  round,  there  must  be  vacant 
spaces  between  them.  If  a  number  of  cannon  balls  were 
placed  in  a  large  vessel  so  as  to  fill  it  up  even  with  the  edge  ; 
though  it  would  hold  no  more  of  tliese  balls,  yet  a  great 
number  of  smaller  shot  might  be  placed  in  the  vacuities  be- 
tween them  :  and  when  the  vessel  would  contain  no  more 
small  shot,  a  great  quanlity  of  sand  might  be  shaken  in,  and 
between  the  pores  of  these,  water  or  other  fluids  would  readily 
insinuate  themselves.  In  a  similar  manner,  a  certain  quan- 
tity of  particles  of  sugar  can  be  taken  up  in  water  without 
increasmg  the  bulk,  and  when  the  water  has  dissolved  the 
sugar,  salt  may  be  dissolved  in  it,  and  yet  the  bulk  remain 
the  same.  And  this  is  easily  accounted  for,  if  we  admit  the 
particles  of  water  to  be  round. 

Fluids  are  either  non-elastic  and  incompressible,  as  water, 
oil,  mercury,  and  others,  or  elastic  and  compressible,  as  air, 
steam,  and  the  different  gases.     The  science  which  treats  of 


48  PRESSURE  OF  FLUIDS. 

the  nature,  gravity,  pressure,  and  motion  of  fluids,  in  general, 
and  of  the  methods  of  weighing  solids  in  them,  is  called  hy- 
drostatics. The  non-elastic  fluids  are  said  to  be  incompres- 
sible, not  because  they  are  absolutely  so,  but  because  their 
compressibility  is  so  very  small  as  to  make  no  sensible  differ 
rence  in  calculations  relative  to  their  several  properties.  It 
has  been  found  that  water  will  find  its  way  through  the  pores 
of  gold,  rather  than  suffer  itself  to  be  compressed  into  a 
smaller  space.  At  Florence,  a  celebrated  city  in  Italy,  a 
globe  made  of  gold  was  filled  with  water,  and  closed  so  ac- 
curately that  none  of  it  could  escape.  The  globe  was  then 
put  into  a  press,  and  a  little  flattened  at  the  sides :  the  con- 
sequence of  which  was,  that  the  water  came  through  the  fine 
pores  of  the  gulden  globe,  and  stood  upon  its  surface  like 
drops  of  dew.  It  was  concluded  at  that  time  that  water  was 
incompressible.  Later  experiments,  however,  have  shown, 
that  those  fluids  which  were  esteemed  incompressible,  are, 
in  a  very  small  degree,  as,  perhaps,  one  part  in  twenty 
thousand,  capable  of  compression. 

Fluids  are  subject  to  the  same  laws  of  gravity  as  solids ; 
but  their  want  of  cohesion  occasions  some  peculiarities.  The 
parts  of  a  solid  are  so  connected  as  to  form  a  whole,  and  their 
weight  is  concentrated  in  a  single  point,  called  the  centre 
of  gravity ;  but  the  atoms  of  a  fluid  gravitate  independently 
of  each  other.  It  is  on  this  account  that  water  always  finds 
its  level ;  for  when  any  particle  accidentally  finds  itself  ele- 
vated above  the  rest,  it  is  attracted  down  to  the  level  of  the 
surface,  and  the  readiness  with  which  water  yields  to  the 
slightest  impression,  will  enable  the  particle  by  its  weight  to 
penetrate  the  surface  and  mix  with  it.  The  particles  of  a 
fluid  acting  thus  independently,  press  against  each  other  in 
every  direction,  not  only  downwards  but  upwards,  and  late- 
rally or  sideways,  and  in  consequence  of  this  equality  of 
pressure,  every  particle  remains  at  rest  in  the  fluid.  If  you 
agitate  the  fluid  you  disturb  this  equality  of  pressure,  and  it 
will  not  rest  till  its  equilibrium  or  level  is  restored.  "The 
pressure  downwards  is  the  effect  of  gravity,  and  if  there  were 
no  lateral  pressure,  water  would  not  run  out  of  an  opening 
on  the  side  of  a  vessel.  The  lateral  pressure  proceeds  entirely 
from  the  downward  pressure,  or  the  weight  of  the  liquid 
above ;  and  consequently  the  lower  an  orifice  is  made  in  a 
yessel,  the  greater  will  be  the  velocity  of  the  water  rushing 


PRESSURE   OP  FLUIDS.  49 

out  of  it.  In  a  cubical  vessel  the  pressure  downwards  will 
be  double  the  lateral  pressure  on  one  side ;  for  every  particle 
at  the  bottom  of  the  vessel  is  pressed  upon  by  a  column  of 
the  whole  depth  of  the  fluid,  whilst  the  lateral  pressure 
diminishes  from  the  bottom  upwards  to  the  surface,  where 
the  particles  have  no  pressure.  The  upward  pressure  of 
fluids  may  be  shown  by  a  machine,  called  the  hydrostatic 
bellows.  It  consists  of  two  oval  or  round  boards,  covered 
with  leather  so  as  to  rise  and  fall  like  the  common  bellows, 
but  without  valves.  A  long  tube  is  fixed  to  the  upper  board 
and  weights  placed  upon  it.  When  the  tube  is  supplied  with 
water,  it  will,  by  its  upward  pressure,  sustain  and  lift  up  the 
weights.  The  pressure  of  water  and  other  fluids  differs  from 
the  gravity  or  weight,  in  this  respect ;  the  weight  is  accord- 
ing to  the  quantity ;  but  the  pressure  is  according  to  the 
Ijerpendicular  height.  Dr.  Goldsmith  relates  that  he  once 
saw  a  strong  hogshead  split  by  the  following  experiment.  A 
strong  small  tube,  made  of  tin,  about  twenty  feet  long,  was 
cemented  into  it,  and  then  water  was  poured  in  to  fill  the 
cask ;  when  it  was  full  and  the  water  had  risen  nearly  to  the 
top  of  the  tube,  the  vessel  burst  with  a  prodigious  force. 
This  extraordinary  power  may  be  greatly  increased  by  a 
forcing  piston  placed  in  the  tube.  A  similar  method  has  been 
adopted  in  forming  a  machine,  called  a  hydrostatic  press,  by 
which  hay  or  cotton  may  be  brought  into  a  compass  twenty 
or  thirty  times  less  than  it  usually  occupies, 

Questions. — 1.  What  is  a  fluid?  2.  What  have  philosophers 
generally  imagined  respecting  the  particles  of  fluids  ?  3.  What  il- 
lustration is  given  respecting  the  vacant  spaces  between  the  parti- 
cles of  fluids  ?  4.  What  are  the  two  kinds  of  fluids  ?  5.  Define 
Hydrostatics.  6.  Why  are  the  non-elastic  fluids  said  to  be  incompres- 
sible .'  7.  Describe  the  experiment  made  at  Florence.  8., What  was 
concludod  at  the  time,  and  what  have  later  experiments  shown  .?  9. 
What  is  the  difference  between  the  gravity  of  fluids  and  solids  .'  10. 
Why  does  water  always  find  its  level  ^  11.  What  is  said  of  the  direc- 
tion in  which  fluids  press  ?  12.  What  is  the  cause  of  the  downward 
and  lateral  pressure  .■*  13.  What  is  said  of  the  lateral  pressure  in  a 
cubical  vessel .'  H.  How  may  the  downward  pregsure  be  shown  i* 
1.5.  How  does  the  pressure  of  a  fluid  differ  from  the  weight*'  16. 
What  is  related  by  Dr.  Goldsmith .?  17.  What  is  said  of  the  hydro- 
static press  ?  18.  Illustrate  the  pressure  of  fluids  by  figures  25.  24. 
and  23.  19  What  is  said  of  what  is  called  the  hydrostatical  paradox .' 
5 


SPECIFIC    GRAVITY   OP    BODIES. 


LESSON  24,  \ 

Specific  Gravity  of  Bodies.  j 

By  the  specific  gravities  of  bodies  we  mean  the  relative  \ 
weights,  which  equal  bulks  of  different  bodies  have  to  each  ' 
other.  And  it  is  usual  to  compare  them  with  that  of  water,  1 
as  it  is  by  weighing  bodies  in  water  that  their  specific  gra-  ] 
vities  are  found.  A  body  immersed  in  a  fluid  will  sink  to  \ 
the  bettom,  if  it  be  heavier  than  its  bulk  of  fluid;  if  it  be  1 
suspended  therein,  it  will  lose  as  muchof  what  it  weighed  in  ^ 
air,  as  its  bulk  of  the  fluid  weighs.  The  instrument  gene»-  \ 
rally  used  for  obtaining  the  specific  gravities  is  called  the  \ 
hydrostatical  balance  ;  it  does  not  differ  much  from  the  com-  \ 
mon  balance.  The  general  rule  for  finding  the  specific  gra-  | 
vity  of  a  solid,  heavier  than  water,  as  a  piece  of  metal,  is  -^ 
this  :  weigh  the  body  first  in  air,  in  the  usual  way,  then 
weigh  it  when  it  is  plunged  in  water,  and  observe  how  much  \ 
it  loses  of  its  weight  in  this  fluid,  and  dividing  the  former.^ 
weight  by  the  loss  sustained,  the  quotient  is  the  specific  gra-  : 
vity  of  the  body,  compared  with  that  of  water.  As  an  ex-  1 
ample,  it  is  usual  to  take  a  guinea,  which  weighs  in  air  one  ■ 
hundred  and  twenty-nine  grains,  and  when  suspended  by  \ 
means  of  a  fine  hair,  and  immersed  in  water,  it  is  found  to  ; 
balance  one  hundred  and  twenty-one  grains  and  three-quar-  \ 
ters,  losing  of  its  weight  seven  grains  and  a  quarter ;  now  \ 
one  hundred  and  twenty-nine  divided  by  seven  and  a  quar-  - 
ter,  gives  about  seventeen  for  the  quotient ;  that  is,  the  spe-  i 
cific  gravity  of  a  guinea  compared  with  that  of  water,  is  as  ' 
about  seventeen  to  one.  And  thus,  any  piece  of  gold  may  \ 
be  tried,  by  weighing  it  first  in  air,  and  then  in  water ;  and  i 
if^  upon  dividing  the  weight  in  air,  by  the  loss  in  water,  the  \ 
quotient  comes  to  be  about  seventeen,  the  gold  is  good ;  if  ] 
the  quotient  be  eighteen,  or  between  eighteen  and  nineteen,  | 
the  gold  is  very  fine ;  but  if  it  be  l.-ss  than  seventeen,  the  ^ 
gold  is  too  much  alloyed  with  some  other  metal.  The  same  ; 
principle  is  universal.  Hence  we  soe  the  reason  why  boats  ] 
or  other  vessels  float  on  water ;  they  sink  just  so  low,  that  j 
the  weight  of  the  vessel,  with  its  contents,  is  equal  to  the  \ 
quantity  of  water  which  it  displaces.  The  method  of  ascer-  ; 
gaining  the  specific  gravities  of  bodies,  was  discovered  by  j 


SPECIFIC    GkAVITY    OF    BODIES.  61 

Archimedes,  in  the  following  manner.  Hifero,  king  of  Sy- 
racuse, having  given  to  a  workman  a  quantity  of  pure  gold, 
of  which  to  make  a  crown,  suspected  that  the  artist  had  kept 
part  of  the  gold,  and  adulterated  the  crown  with  a  baser 
metal.  The  king  applied  to  Archimedes  to  discover  the 
fraud.  The  philosopher  long  studied  it  in  vain,  and  at  length 
accidentally  hit  upon  a  method  of  verifying  the  king's  sus- 
picion. Going  one  day  into  a  bath,  he  took  notice  that  the 
water  rose  in  the  bath,  and  immediately  reflected  that  any 
body,  of  equal  bulk  with  himself,  would  have  raised  the  water 
just  as  much ;  though  a  body  of  equal  weight,  but  not  of 
equal  bulk,  would  not  raise  it  so  much.  From  this  idea  he 
conceived  a  mode  of  finding  out  what  he  so  much  wished, 
and  was  so  transported  with  joy,  that  he  ran  out  of  the  bath, 
crying  out  in  the  Greek  tongue,  "  I  have  found  it,  I  have 
found  it !" 

Now,  since  gold  was  the  heaviest  of  all  metals  known  to 
Archimedes,  it  occurred  to  him  that  it  must  be  of  less  bulk, 
according  to  its  weight,  than  any  other  metal ;  and  he,  there- 
fore, desired  that  a  mass  of  pure  gold,  equally  heavy  with 
the  crown  when  weighed  in  air,  should  be  weighed  against 
it  in  water,  conjecturing  that  if  the  crown  was  not  alloyed, 
it  would  counterpoise  the  mass  of  gold  when  they  were  both 
immersed  in  water,  as  well  as  it  did  when  they  were  weighed 
in  air.  But  upon  making  trial,  it  was  found  that  the  mass 
of  gold  weighed  much  heavier  in  water  than  the  crown  did  : 
nor  was  this  all — when  the  mass  and  crown  were  immersed 
separately  in  the  same  vessel  of  water,  the  crown  raised  the 
water  much  higher  than  the  mass  did  ;  which  showed  it  to 
be  alloyed  with  some  lighter  metal  that  increased  its  bulk. 
And  upon  this  principle  is  the  doctrine  of  the  specific  gravi- 
ties of  bodies  founded. 

Questions. — 1.  What  is  meant  by  the  specific  gravities  of  bodies  i* 
2.  What  is  said  of  a  body  immersed  in  a  fluid  ?  3.  What  is  the  gene- 
ral rule  for  finding  the  specific  gravity  of  a  solid  heavier  than  water  ? 
4.  What  example  is  given  ?  5.  How  may  a  piece  of  gold  be  tried  ? 
6.  Why  do  vessels  float  ?  7.  What  incident  led  to  the  method  of  dis- 
covering the  specific  gravities  of  bodies  ?  8.  Who  made  the  disco- 
very, and  how  ?  9.  Explain  the  method  and  the  result.  10.  Explain 
by  fig.  14.  the  use  of  the  hydrostatic  balance.  11.  Describe  the  hy* 
droineter. 


THE    SYPHON. 


LESSON  25. 

Jli/draulics. 

Intermittent,  coming  by  fits,  not  constant. 
Res'ervoir,  a  conservatoiy  of"  water  ;  a  store. 
VaCuum,  a  space  unoccupied  by  mattef. 

The  science  of  Hydraulics  teaches  how  to  estimate  the 
Velocity  and  force  of  fluids  in  motion.  Upon  the  principle 
of  this  science  all  machines  worked  by  water  are  constructed, 
as  engines,  mills,  pumps,  and  others.  Water  can  be  set  in 
motion  by  its  own  gravity,  as  when  it  is  allowed  to  descend 
from  a  higher  to  a  lower  level ;  and  by  an  increased  pressure 
of  the  air,  or  by  removing  the  pressure  of  the  atmosphere, 
it  will  rise  above  its  natural  level.  In  the  former  case  it 
will  seek  the  lowest  situation,  and  in  the  latter,  it  may  be 
forced  to  almost  any  height. 

The  syplwii  is  a  pipe  used  to  draw  off  water,  wine,  or  other 
fluids,  from  vessels  which  it  would  be  inconvenient  to  move 
from  the  place  in  which  they  stand.  It  is  made  of  tin  or 
copper,  and  bent  in  such  a  manner  that  one  limb  may  reach 
down  through  the  hole  in  the  top  of  the  vessel  to  be  emptied, 
to  its  very  bottom ;  the  other  limb  should  be  the  longest,  so 
that  when  filled  it  may  contain  a  heavier  body  of  fluid  than 
tliat  within  the  vessel.  The  pressure  of  the  atmosphere  being 
taken  off  from  that  part  of  the  surface  of  the  liquor  within 
the  tube,  the  liquor  rises  above  its  natural  level,  and  flows 
through  the  longer  liuib,  and  the  contents  of  the  vessel  are 
drawn  off  to  the  last.  There  are  intermittent  springs  in  va- 
rious places  of  the  woi'Id,  which  have  been  explained  on  the 
principle  of  the  syphon.  A  passage  for  the  water  may  have 
been  formed  in  the  soil,  and  when  the  internal  cavity  has 
been  filled  witli  water,  so  as  to  begin  to  run  off  by  this  passage, 
the  pressure  of  the  atmosphere  will  make  the  water  flow  till 
all  is  carried  off.  Of  course  the  spring  then  ceases  until  the 
cavity  is  again  filled  with  water,  when  the  same  phenomenon 
is  repeated.  Fluids  may  be  conveyed  over  hills  and  valleys 
in  bent  pipes,  to  any  height  which  is  not  greater  than  the 
level  of  the  spring  whence  they  flow.  The  Romans,  either 
from  their  ignorance  of  the  pressure  of  fluids,  or  from  their 
love  of  magnificence,   conveyed    water    across  valleys  by 


FORCING   PUMP. 


53 


straight-lined  aqueducts,  wliich  were  supported  by  immense 
arches  or  columns. 

The  common  pump  consists  of  a  large  tube  or  pipe,  called 
the  barrel,  whose  lower  end  is  immersed  in  the  water  which 
it  is  designed  to  raise.  A  kind  of  stopper,  called  a  piston, 
is  fitted  to  this  tube,  and  is  made  to  slide  up  and  down  by 
means  of  a  metallic  or  wooden  rod.  In  the  piston,  there  is 
a  valve,  or  little  door,  which  opening  upwards,  admits  the 
water  to  rise  through  it,  but  prevents  its  returning.  A  simi- 
lar valve  is  fixed  in  the  body  of  the  pump.  When  the  pump 
is  in  a  state  of  inaction,  the  two  valves  are  closed  by  their 
own  weight ;  but  when  the  piston  is  made  to  ascend,  it 
raises  a  column  of  air  which  rested  upon  it,  and  produces  a 
vacuum  between  itself  and  the  lower  valve;  the  air  beneath 
this  valve  expands  and  forces  its  way  through  it ;  and  the 
water,  relieved  from  the  pressure  of  air,  ascends  into  the 
pump,  being  forced  up  by  the  weight  of  the  surrounding 
atmosphere.  When  the  piston  now  descends  it  is  forced 
into  the  water,  which,  as  it  cannot  repass  through  the  lower 
valve,  must  rise  through  the  valve  of  the  moveable  piston,  by 
the  ascent  of  which,  it  is  lifted  up  and  runs  off  at  the  spout. 
There  must  never  be  so  great  a  distance  as  thirty-three  feet 
from  the  level  of  the  water  in  the  well,  to  the  valve  in  the 
piston,  for  in  that  case,  the  water  would  not  rise  through  the 
valve,  because  the  pressure  of  the  atmosphere  will  not  sus- 
tain a  column  of  water  above  that  height.  But  when  the 
water  has  passed  the  valve  in  the  moveable  piston,  it  is  not  the 
pressure  of  the  air  on  the  reservoir  which  makes  it  ascend ; 
it  is  raised  by  lifting  it  up,  as  you  would  raise  it  in  a  bucket, 
of  which  the  piston  formed  the  bottom. 

The  forcing  pump  is  not  only  used  to  raise  water  from  a 
well  to  the  surface  of  the  earth,  but  likewise  to  force  it  into 
reservoirs  on  the  tops  of  buildings,  from  which  pipes  are  laid 
to  convey  it  to  different  parts  as  conveniency  requires.  It 
differs  from  the  common  pump  by  having  the  upper  piston 
solid,  and  a  pipe  joined  to  the  barrel  just  above  the  lower 
piston,  through  which  the  water  passes  into  what  is  termed 
the  air  vessel.  In  the  pipe  which  leads  to  the  air  vessel 
there  is  a  fixed  valve,  which  opens  upwards  and  prevents  the 
return  of  the  water.  Through  the  upper  part  of  the  air 
vessel  a  tube  is  inserted,  which  reaches  nearly  to  its  bottom. 
Now  the  air  which  is  above  the  water  in  the  vessel  being 
5* 


64  THE    DIVING    hT.tt. 

confined,  and  condensed  into  a  smaller  bulk  than  its  "hatiifal 
space,  presses  by  its  elasticity  upon  the  surface  of  the  water, 
and  forces  it  violently  up  the  tube  in  a  continual  stream.  It 
is  ujpon  this  principle  that  the  engine  for  extinguishing  fires 
is  constructed. 

Questions. — 1.  What   does  the  science  of  hydraulics  teach  ?     2. 
What  machines  are  constructed  on  the   principles  of  this  science.-* 

3.  What  are  the  diflerent  ways  in  which  water  may  be  sot  in  motion  ?^ 

4.  What  is  the  syphon  ?  5.  Describe  the  manner  of  its  conveying 
fluids.  6.  How  are  intermittent  springs  caused  ?  7.  Describe  the 
common  pump  and  show  how  it  raises  water.  8.  How  high  can  water 
be  raised  in  a  common  pump?  9.  Describe  the  forcing  pump.  10. 
What  engine  is  constructed  on  the  principle  of  the  forcing  pump  ? 
11.  Describe  the  common  pump  by  fig.  21.  and  show  its  action.  12. 
Forcing  pump  by  fig.  22.  and  show  how  it  acts  in  forcing  up  water. 


LESSON  26. 
The  Diving  Bell,  and  Steam  Engine, 

Ver'tically,  in  a  direction  perpendicular  to  the  horizon. 
Appara'tus,  utensils  and  appendagea  belonging  to  a  machine. 

If  you  take  a  glass  tumbler,  and  plunge  it  in  water  with 
the  mouth  downwards,  you  will  perceive  that  very  little  water 
will  enter  into  it.  The  air  which  fills  the  glass  prevents  the 
entrance  of  the  water  ;  but  as  air  is  compressible,  it  cannot 
entirely  exclude  the  water,  which,  by  its  pressure,  condenses 
the  air  in  a  slight  degree.  Upon  this  simple  principle  ma- 
chines have  been  invented,  by  v/hich  people  have  been  abid 
to  walk  about  at  the  bottom  of  the  sea,  with  as  much  safety 
as  upon  the  surface  of  the  earth.  The  original  instrument 
of  this  kind  was  much  improved  by  Dr.  Halley,  more  than  a 
century  ago.  The  machine  was  made  of  copper  in  the  shape 
of  a  bell.  The  diameter  of  the  bottom  was  five  feet,  that 
of  the  top  three  feet,  and  it  was  eight  feet  high.  To  make 
the  vessel  sink  vertically  in  water,  the  bottom  was  loaded 
with  a  quantity  of  leaden  balls.  Light  was  let  into  the  bell 
by  means  of  strong  spherical  glasses  fixed  in  the  top.  Barrels, 
filled  with  fresh  air,  were  made  sufficiently  heavy,  and  sent 
down,  from  which  a  leathern  pipe  communicated  with  the 
inside  of  the  bell,  and  a  tube  with  a  stop  at  the  upper  part 
let  out  the  air  which  had  become  unfit  for  breathing.     The 


STEAM    ENGINE.  55 

dtvers  are  generally  let  down  from  a  ship,  and  taking  a  rope 
with  them,  to  which  is  fixed  a  bell  in  the  vessel,  they  have 
only  to  pull  the  string,  and  the  people  in  the  ship  draw  them 
up  ;  but  if  business  requires  it,  they  will  stay  several  hours 
at  the  bottom  of  the  sea  without  the  smallest  difficulty.  By 
means  of  a  strong  globular  cap  with  circular  glasses  in  front 
to  give  light,  it  has  been  found  practicable  for  a  diver  to  go 
out  of  the  engine  to  the  distance  of  eighty  or  a  hundred 
yards,  the  air  being  conveyed  to  him  in  a  continued  stream 
by  small  flexible  pipes.  Accidents,  which  through  careless-* 
ness  have  sometimes  occurred,  may  be  readily  prevented,  by 
a  proper  degree  of  attention,  and  people  may  descend  to  very 
great  depths  without  danger.  The  diving  bell  has  often 
been  used  in  bringing  up  the  goods  from  a  vessel  which  has 
sunk  in  deep  water,  and  in  blowing  rocks  which  impeded 
navigation. 

The  Steam  Engine  is  one  of  the  most  useful,  curious,  and 
important  machines  that  have  ever  been  invented.  It  con- 
sists of  a  large  cylinder  or  barrel,  in  which  is  fitted  a  solid 
piston  like  that  of  the  forcing  pump.  Steam  is  supplied  from 
a  large  boiler,  which  in  forcing  up  the  piston,  instantly  opens 
a  valve,  through  which  cold  water  rushes,  on  the  principle 
of  the  common  pump.  Other  steam  is  then  introduced 
above  the  piston,  which  forces  it  down,  and  drives  the  water 
out  of  the  pipe.  Steam  raises  the  piston  again,  and  agai;: 
makes  it  fall,  and  thus  produces  an  alternate  motion,  which 
is  communicated,  by  an  upright  iron  rod,  to  a  large  beam  or 
lever,  that  is  lifted  up  and  pulled  down  with  wonderful  pre- 
cision and  force.  This  regular  and  powerful  motion  is  easily 
applied  by  the  mechanic  to  all  kinds  of  machinery.  The 
apparatus  has  been  varied  by  diflferent  persons,  and  for  diffe- 
rent objects  ;  but  the  principle  remains  the  same. 

By  the  admirable  contrivances  of  Watt  and  Fulton,  the 
steam-engine  has  become  a  thing  stupendous  alike  for  its 
force  and  flexibility, — for  the  prodigious  power  which  it  can 
exert,  and  the  ease,  and  precision,  and  ductility  with  which 
it  can  be  varied,  distributed,  and  applied.  The  trunk  of  an 
elephant,  that  can  pick  up  a  pin  or  rend  an  oak,  is  nothing 
to  it.  It  can  engrave  a  seal,  and  crush  masses  of  obdurate 
metal  before  it,— draw  out,  without  breakings  a  thread  as 
fine  as  gossamer,  and  lift  up  a  ship  of  war  like  a  bauble  in 
the  air.     It  can  embroider  muslin  and  forge  anchors, — cut 


B6  NATURE    AND    PROPERTIES    OF    AIR. 

Steel  into  ribands,  and  impel  loaded  vessels  against  the  fury 
of  the  winds  and  waves.  It  has  armed  tlie  feeble  hand  of 
man,  in  short,  with  a  power  to  which  no  limits  can  be  as- 
signed ;  completed  the  dominion  of  mind  over  the  most  re- 
fractory qualities  of  matter  ;  and  laid  a  sure  foundation  for 
all  those  future  miracles  of  mechanic  power  which  are  to 
aid  and  reward  the  labour  of  after  generations. 

Questions. — 1.  What  is  the  principle  of  the  diving  bell  ?  2.  What 
were  the  dimensions  of  Dr.  IJalloy's  diving  bell .'  3.  How  was  light 
let  in -^  4.  Fresh  air?  5.  How  do  divers  make  known  tlieir  wish  to 
be  drawn  up  ?  6.  Of  what  use  is  tliis  invention  ?  7.  Describe  the 
steam-engine. 


LESSON  27. 

Nature  and  Properties  of  Air. 

Den'sity,  the  degree  of  closeness  and  compactness  of  the  parti- 
cles of  a  body,  tlie  property  directly  opposite  to  rarity. 
Ab'solutely,  completely,  without  restriction,  positively. 
Hem'isphere,  lialf  a  globe,  or  sphere. 

The  science  which  treats  of  the  mechanical  properties  of 
elastic  or  aeriform  fluids,  such  as  tlieir  weight,  density,  com- 
pressibility, and  elasticity,  is  called  Pneumatics.  The  air  in 
which  we  live  surrounds  the  eartli  to  a  considerable  height, 
revolves  with  it  in  its  diurnal  and  annual  motion,  and,  toge- 
ther with  the  clouds  and  vapours  that  float  in  it,  is  called  the 
atmosphere.  The  height  to  which  the  atmosphere  extends 
has  never  been  ascertained  ;  but  at  a  greater  height  than 
forty-five  miles  it  ceases  to  reflect  the  rays  of  light  from  the 
sun.  The  air  is  invisible  because  it  is  perfectly  transparent ; 
but  it  may  be  felt  on  moving  the  hand  in  it,  or  when  it 
moves  and  produces  what  we  call  wind.  It  is  nearly  nine 
hundred  times  lighter  than  water,  but  the  whole  atmosphere 
presses  on  all  sides  like  other  fluids,  upon  whatever  is  im- 
mersed in  it,  and  in  proportion  to  the  depths.  Its  pressure 
upon  a  mountain  is  known  to  be  less  than  in  the  plain  or 
valley  beneath.  If  a  alass  tumbler  be  completely  filled  with 
water,  and  covered  wth  a  piece  of  writing  paper,  so  as  to 
hold  it  tight,  and  accurately  even,  the  water  will  not  run  out 
although  the  glass  be  iuverteci  and  the  hand  removed.    The 


AIR   PU5IP.  57 

weight  of  the  water  is  sustained  by  the  upward  pressure  of 
the  air  upon  the  paper. 

The  most  essential  point  in  which  air  differs  from  other 
fluidSj  is  by  its  spring  or  elasticity,  that  is  to  say,  its  power 
of  increasing  or  diminisliing  in  bulk,  according  as  it  is  more 
Or  less  compressed.  The  elasticity  of  air  differs  from  that  of 
bodies  in  general ;  for  when  solid  bodies  are  compressed 
they  have  an  elastic  power,  which  causes  them  to  resume 
the  same  figure  they  possessed  before  compression  :  but  on 
removing  the  pressure  on  air,  it  will  not  only  resume  its  first 
bulk,  but  expand  to  an  indefinite  extent.  With  regard  to 
animal  and  vegetable  bodies,  the  gravity  of  the  air  is  de- 
stroyed by  its  elasticity.  It  is  true,  that  the  atmosphere  presses 
with  a  weight  of  fifteen  pounds  upon  every  square  inch  of 
the  earth's  surface,  when  the  air  is  heaviest,  and  tliat  conse- 
quently a  man's  body,  which  contains  nearly  fifteen  square 
feet,  will  sustain  a  weight  equal  to  about  fourteen  tons  and  a 
half;  but  this  pressure  is  so  great  that  it  would  be  absolutely 
insupportable,  and  even  fatal  to  us,  were  it  not  equal  in 
every  part,  and  counterbalanced  by  the  spring  of  that  air 
which  fills  all  the  vesicles  of  the  body,  and  reacts  with  an 
outward  force  equal  to  that  with  which  the  atmosphere 
presses  inward. 

By  means  of  an  air-pump,  the  air  may  be  drawn  out  of  a 
large  glass  vessel,  or  receiver,  and  a  vacuum  produced,  in 
which  a  great  number  of  curious  experiments  may  be  per- 
formed, showing  at  once  the  properties  and  usefulness  of  the 
air.  We  shall  give  a  brief  description  of  the  air-pump, 
though  a  view  of  the  machine  itself  will  convey  a  much  bet- 
ter idea  of  the  important  purposes  to  which  it  is  applied,  than 
any  description  can  afford-  Two  brass  cylinders  are  closely 
and  firmly  fastened  down  to  the  table  or  base  of  the  machine, 
by  means  of  what  are  called  the  head  and  the  columns.  The 
receiver  is  made  to  fit  very  accurately  on  a  brass  circular 
plate,  which  has  a  hole  in  the  middle,  through  which  the 
air  passes  from  the  receiver  into  a  tube  made  of  brass,  that 
communicates  with  the  cylinders.  Near  the  bottom  of  each 
cylinder  is  a  valve  opening  upwards,  and  above  these  valves 
are  two  others  in  pistons  which  are  moved  up  and  down  by 
toothed  rods  that  fall  into  a  toothed  wheel,  to  the  axis  of 
which  a  handle  is  fixed.  On  turning  the  handle  one  of  the 
pistons  is  raised  and  the  other  depressed,  consequently  a  ra- 


S8  CONDENSING    SYRINGli. 

refied  space  is  formed  between  the  upper  and  lower  valve  m 
one  cylinder ;  then  the  air  which  is  contained  in  the  receiver 
rushes  through  the  brass  tube  and  by  its  elasticity  forces 
up  the  lower  valve  and  enters  the  cylinder ;  then  the  valve 
closes  and  prevents  the  air  from  returning  into  the  receiver. 
When  the  motion  is  reversed,  the  other  piston  ascends,  and 
the  first  is  depressed  ;  in  its  depression,  the  elasticity  of  the 
air  contained  between  the  two  valves,  forces  open  the  up 
permost  valve,  and  it  escapes  into  the  upper  part  of  the  cy- 
linder ;  then  the  valve  closes  and  prevents  its  return.  Whilst 
one  piston,  therefore,  exhausts  the  air  from  the  receiver,  the 
other  is  discharging  it  from  the  top  of  the  cylinder.  Thus 
by  continued  exhaustion,  the  density  of  the  air  keeps  de- 
creasing in  the  receiver,  till  its  elasticity  is  no  longer  able  to 
force  up  the  lower  valves,  which  terminates  the  effect  of  the 
machine.  The  air  is  admitted  into  the  receiver  again  by 
unscrewing  a  small  nut  which  is  so  situated  as  to  comniuni* 
cate  with  the  air  channel. 

If  the  air  be  exhausted  from  a  receiver,  it  will  be  held 
fast  by  the  pressure  of  the  external  air.  If  a  small  receiver 
be  placed  under  a  larger,  and  both  exhausted,  the  larger 
will  be  held  fast,  while  the  smaller  will  be  easily  moved.  If 
a  guinea  and  a  feather  be  dropped  from  the  top  of  the  re- 
ceiver, they  will  reach  the  bottom  at  the  same  instant,  be- 
cause there  is  then  no  resisting  medium.  Animals  cannot 
live  in  an  exhausted  receiver,  and  the  continuance  of  life 
varies  according  to  the  strength  or  size  of  the  animal.  A 
man  requires  a  gallon  of  fresh  air  every  minute.  If  a  lighted 
candle  be  covered  with  a  receiver  containing  a  gallon  of  air, 
the  candle  will  burn  a  minute  ;  and  then  the  flame,  after 
having  gradually  decayed,  will  go  out.  A  constant  supply 
of  fresh  air,  therefore,  is  as  necessary  to  feed  flame  as  to 
support  life.  If  two  brass  hemispheres  of  three  or  four 
inches  in  diameter  be  put  together,  and  the  internal  air  ex- 
hausted, the  pressure  from  without  will  require  one  hundred 
and  fifty  pounds  to  separate  them ;  but  if  the  external  air 
fee  taken  away,  they  wilr  separate  of  themselves. 

The  Condensing  Syringe  has  a  solid  piston,  and  a  valve 
in  the  lower  part  of  its  barrel  which  opens  downwards.  By 
thrusting  down  the  piston  the  air  is  forced  through  the  valve, 
which  is  afterwards  held  close  by  the  elasticity  of  the  con- 
densed air.    When  the  piston  is  raised  up  a  vacuum  is  pro- 


THE   BAROMETER.  S# 

duced,  till  it  is  raised  above  a  small  hole  in  the  barrel,  when 
the  air  rushes  in,  and  is  again  discharged  through  the  valve, 
An  instrument  of  this  kind  is  used  to  produce  what  is  called 
the  artificial  fountain. 

Questions. — 1.  What  is  Pneumatics  ?  2.  What  is  the  atmosphere  ? 
3.  What  is  said  of  its  height  ?  4.  What  is  wind  ?  5.  What  is  said 
of  the  weight  and  pressure  of  the  atmosphere  ?  6.  What  experiment 
illustrates  the  upward  pressure  of  the  atmosphere  ?  7.  How  does  the 
elasticity  of  air  differ  from  the  elasticity  of  bodies  in  general  ?  8. 
What  is  the  weight  of  the  atmosphere  upon  a  square  inch  ?  9.  Upon 
the  surface  of  a  man's  body  ?  10.  How  is  the  pressure  of  the  air  upon 
the  body  counterbalanced.'  11.  Describe  the  air-pump.  12.  Show 
the  method  by  which  the  air  is  drawn  from  the  receiver.  13.  What 
are  some  of  the  experiments  that  may  be  performed  by  an  air-pump  ? 
14.  Describe  the  condensing  syringe,  and  its  action.  15.  Look  at  fig. 
16.  and  describe  the  air-pump,  and  show  its  action.  IG.  Look  at  fig. 
26.  and  describe  the  artificial  fountain. 


LESSON  28. 

The  Barometer. 

Hermet'ically,  a  term  applied  to  the  closing  of  the  orifice  of  a 
glass  tube  by  fusion,  so  as  to  render  it  air-tight. 

Respira'tion,  the  act  of  alternately  inspiring  air  into  the  lungs,  and 
expiring  it  from  them. 

The  Barometer  is  a  very  useful  instrument  for  determin- 
ing the  variations  of  the  weather.  If  a  glass  tube  of  about 
thirty-two  or  thirty-three  inches  long,  hermetically  sealed  at 
one  end,  be  filled  with  mercury,  and  then  inverted  in  a  basin 
or  cup  of  the  same  fluid,  the  mercury  in  the  tube  will  stand 
at  an  altitude  above  the  surface  of  that  in  the  basin  between 
twenty-eight  and  thirty-one  inches.  The  tube  and  the  basin 
are  fixed  on  a  board,  for  the  convenience  of  suspending  it; 
the  board  is  graduated  for  the  purpose  of  ascertaining  the 
height  at  which  the  mercury  stands  in  the  tube  ;  and  a  small 
moveable  metallic  plate,  called  a  vernier,  an  inch  of  which 
is  divided  into  a  hundred  equal  parts,  serves  to  show  that 
height  with  greater  accuracy.  The  height  at  which  the 
mercury  will  stand  depends  upon  the  weight  of  the  atmo- 
sphere, which  varies  much  according  to  the  state  of  the  wea- 
ther. The  air  is  heaviest  in  dry  weather,  for  it  is  then  that 
the  mercury  is  found  to  rise  in  the  tube  and  consequently 


60 


THE    BAROMETER. 


the  mercury  in  tlic  cup  must  be  most  pressed  by  the  air.  It  I 
is  true  that  in  damp  weather  the  air  feels  heaviest,  but  it  is  i 
on  account  of  its  being  less  salubrious.  The  lungs  under  , 
these  circumstances  do  not  play  so  freely,  nor  does  the  blood  ] 
circulate  so  well ;  and  thus  obstructions  are  frequently  occa-  j 
sioned  in  the  smaller  vessels,  from  which  arise  colds,  asthmas,  j 
and  fevers.  The  thinness  of  the  air  in  elevated  situations  ] 
is  sometimes  oppressive  from  being  insufficient  for  respira-  : 
tion ;  and  the  expansion  which  takes  place  in  the  more  ; 
dense  air  contained  within  the  body  is  often  painful.  It  oc-  ; 
casions  distension,  and  sometimes  causes  the  bursting  of  J 
smaller  blood-vessels.  ,'i 

The  barometer  has  been  used  for  the  purpose  of  measur-   I 
ing  the  heights  of  mountains  and  towers,  and  of  estimating  ] 
the  elevation  of  balloons.     The  weight  of  one  hundred  and   I 
three  feet  of  air  is  equal  to  that  of  one  tenth  of  an  inch  of   j 
mercury.    If  a  barometer,  therefore,  be  carried  to  any  great  ' 
eminence,  the  mercury  will  descend  one  tenth  of  an  inch  for    ; 
every  one  hundred  and  three  feet  that  the  barometer  ascends,   j 
When  the  surface  of  the  mercury  is  convex,  or  stands  higher   ] 
in  the  middle  than  at  the  sides,  it  is  a  sign  the  mercury  is   ^ 
then  in  a  rising  state  ;  but  if  the  surface  be  concave,  or  hollow    ] 
in  the  middle,  it  is  then  sinkiag.     In  very  hot  weather,  the    ^ 
falling  of  the  mercury  indicates  thunder.     In  winter,  the    = 
rising  indicates  frost,  and  in  frosty  weather  if  the  mercury    ; 
falls  three  or  four  divisions,  there  will  be  a  thaw.     But  in  a    ■ 
continued  frost,  if  the  mercury  rises,  it  will  snow.     In  wet 
weather,    when  the  mercury  rises  much   and  high,   and  so    \ 
continues  for   two  or  three  days   before  the  bad   weather  is    \ 
entirely  over,  then  a  continuance  of  fair  weather  may  be  ex-  ^ 
pected.     In  fair  weather,  when  the  mercury  falls  low,  and    i 
thus  continues  for  two  or  three  days  before  the  rain  comes, 
then  much  wet  weather  may  be  expected  and  probably  high    '^ 
winds.     The  unsettled  motion  of  the  mercury  denotes  un-   < 
settled  weather.    The  words  engraved  on  the  scale  are  not 
so  much  to  be  attended  to,  as  the  rising  and  falling  of  the    1 
mercury.     It  always  sinks  lowest  of  all  for  great  winds,    • 
though  not  accompanied  with  rain;  but  it  falls  more  for 
wind  and  rain  together  than  for  either  of  them  alone.     Ba- 
rometers are  frequently  made  of  a  tube  with  a  curved  neck 
and  bulb,  being  more  commodious  than  the  basin  and  tube. 
^0  make  these  tolerably  exact,  however,  the  circular  are^ 


SOUND.  61 

of  the  bulb  should  be  at  least  thirty  or  forty  times  larger  than 
that  of  the  tube ;  so  that  the  mass  of  mercury  may  be  as 
little  affected  as  possible  whilst  it  rises  and  falls  ;  for  the 
height  of  the  column  is  taken  from  the  surface  of  the  mer- 
cury in  the  bulb  to  its  height  in  the  tube. 

Questions. — 1.  What  is  the  construction  of  the  barometer  ?  2. 
Upon  what  does  the  height  of  tlie  mercury  depend  ?  3.  Why  is  the 
air  heaviest  in  dry  weather  ?  4.  Why  does  it  feel  heaviest  in  damp 
weather  ?  5.  How  may  the  height  of  a  mountain  be  ascertained  by 
the  barometer?  6.  What  is  indicated  by  the  convexity  and  concavity 
of  the  mercury  ?  7.  Upon  what  other  construction  are  barometere 
made  than  that  first  described  ? 


LESSON  29. 

Sound. 

Humid'ity,  moisture.  The  degrees  of  moisture  in  the  air  are 
measured  by  an  instrument  called  a  Hygrom'eter,  of  which 
there  are  various  kinds  ;  whatever  contracts  or  expands  by 
the  moisture  or  dryness  of  the  atmosphere  is  capable  of  being 
formed  into  one. 

Sound  arises  from  a  tremulous  or  vibrating  motion  in  elas- 
tic bodies,  which  is  caused  by  a  stroke  or  collision,  and  is 
carried  to  the  ear  through  the  medium  of  the  air.  The  pro- 
duction of  sound  therefore  depends  upon  three  circumstan- 
ces, a  sonorous  body  to  give  the  impression,  a  medium  to 
convey  it,  and  the  ear  to  receive  it.  Sonorous  bodies,  how- 
ever, are  merely  the  instruments  by  which  a  peculiar  species 
of  motion  is  communicated  to  the  air.  It  is  true  that  when  you 
ring  a  bell,  both  the  bell  and  the  air  are  concerned  in  the  pro- 
duction of  sound  :  but  sound,  strictly  speaking,  is  a  perception 
excited  in  the  mind  by  the  motion  of  the  air  on  the  nerves 
of  the  ear ;  the  air,  therefore,  as  well  as  the  sonorous  bodies 
which  put  it  in  motion,  is  only  the  cause  of  soimd, — the  im- 
mediate effect  is  produced  by  the  sense  of  hearing :  I5r 
without  this  sense,  there  would  be  no  sound.  The  vibrating 
air  strikes  the  ear,  and  causes  in  the  mind  the  perception  of 
sound. 

If  you  endeavour  to  ring  a  small  bell,  after  you  have  sus- 
pended it  under  the  receiver  in  an  air-pump,  from  which 
the  air  has  been  exhausted,  no  sound  will  be  produced.  By 
6 


63  VELOCITY    OF    SOUND. 

exhausting  the  receiver,  you  cut  off  the  communication  be- 
tween the  air  and  bell ;  and  the  latter,  therefore,  cannot 
impart  its  motion  to  the  air.  It  has  been  ascertained  that 
liquids  as  well  as  air  are  capable  of  conveying  the  vibratory 
motion  of  a  sonorous  body  to  the  organ  of  l>earing  ;  for 
sound  can  be  heard  under  water.  Dr.  Franklin  imagined, 
that  with  his  ear  under  water,  he  heard  the  collision  of 
stones  in  that  medium,  at  the  distance  of  a  mile. 

The  vibration  of  a  sonorous  body  gives  a  tremulous  mo- 
tion to  the  air  around  it,  very  similar  to  the  motion  commu- 
nicated to  smooth  water  when  a  stone  is  thrown  into  it. 
This  first  produces  a  small  circular  wave  around  the  spot  in 
which  the  stone  falls  ;  the  wave  spreads,  and  gradually  com- 
municates its  motion  to  the  adjacent  waters,  producing  simi- 
lar waves  to  a  considerable  extent.  The  same  kind  of  waves 
are  produced  in  the  air  by  the  motion  of  a  sonorous  body, 
but  with  this  difference,  that  as  air  is  an  elastic  fluid,  the 
motion  does  not  consist  of  regularly  extending  waves,  but  of 
vibrations,  and  are  composed  of  a  motion  forwards  and  back- 
wards, similar  to  those  of  a  sonorous  body.  They  differ  also 
in  the  one  taking  place  in  a  plane,  the  other  in  all  directions  : 
the  aerial  undulations  being  spherical.  The  first  sphere  of 
undulations  .^jvhich  are  produced  immediately  round  the  so- 
norous body,  by  pressing  against  the  contiguous  air,  con- 
denses it.  The  condensed  air,  though  impelled  forward  by 
the  pressure,  reacts  on  the  first  set  of  undulations,  driving 
them  back  again.  The  second  set  of  undulations  which 
have  been  put  in  motion,  in  their  turn  communicate  their 
motion,  and  are  themselves  driven  back  by  reaction.  Thus 
there  is  a  succession  of  waves  in  the  air,  corresponding  with 
the  succession  of  waves  in  the  water. 

The  air  is  a  fluid  so  much  less  dense  than  water,  that 
motion  is  more  easily  comiimnicated  to  it.  The  firing  of  a 
cannon  produces  vibrations  of  the  air  which  extend  to  se- 
veral miles  around.  Distant  sound,  however,  takes  some 
time  to  reach  us,  and  we  see  the  light  of  the  flash  long  be- 
fore we  hear  the  report.  The  velocity  of  sound  is  commonly 
computed  at  the  rate  of  eleven  hundred  and  forty-two  feet 
in  a  second.  Its  velocity  varies  according  to  the  tempe- 
rature, density,  and  humidity  of  the  atmosphere.  It  is  in- 
fluenced also  by  the  force  and  direction  of  the  wind.  The 
velocity  of  sound  has  been  applied  to  the  measurement  of 


£CHO.  68 

tlistances;  If  a  ship  at  sea  in  distress  fires  a  gun,  the  light 
of  which  is  seen  on  shore  twenty  seconds  before  the  report 
is  heard,  it  is  therefore  known  to  be  at  the  distance  of  twenty 
times  eleven  hundred  and  forty-two  feet,  or  a  little  more  than 
four  miles  and  one  third.  By  counting  the  number  of  seconds 
elapsed  between  the  flash  of  lightning  and  the  clap  of 
thunder,  you  may  ascertain  how  far  distant  you  are  from 
the  cloud. 

When  the  aerial  vibrations  meet  with  an  obstacle,  having 
a  hard  and  regular  surface,  such  as  a  wall  or  rock,  they  are 
reflected  back  to  the  ear,  and  produce  the  same  sound  a 
second  time  ;  but  the  sound  will  then  appear  to  proceed  from 
the  object  by  which  it  is  reflected.  If  the  vibrations  fall 
perpendicularly  on  the  obstacle,  they  are  reflected  back  in 
the  same  line  ;  if  obliquely,  the  sound  returns  obliquely  in 
the  same  direction.  This  reflected  sound  is  called  an  echo. 
At  Rosneath,  near  Glasgow,  there  is  an  echo  that  repeats  a 
tune,  played  with  a  trumpet,  three  times,  completely  and 
distinctly.  At  Brussels  there  is  an  echo  that  answers  fifteen 
times ;  and  in  Italy,  near  Milan,  the  sound  of  a  pistol  is  re- 
turned fifty-six  times.  Speaking  trumpets,  and  those  made 
to  assist  the  hearing  of  deaf  persons,  depend  on  the  reflec- 
tion of  sound  from  the  sides  of  the  trumpet,  and  also  by  its 
being  confined  and  prevented  from  spreading  in  every  di- 
rection. 

Questions. — 1.  From  what  does  sound  arise  ?  2.  Upon  what  three 
circumstances  does  the  production  of  sound  depend  ?  3.  What  is 
sound,  strictly  speaking  ?  4.  How  can  it  be  shown  that  air  is  neces- 
sary to  the  production  of  sound  ?  5.  Why  cannot  a  bell  be  heard  in 
an  exhausted  receiver  ?  6.  What  are  conductors  of  sounds  besides  the 
atmosphere  ?  (Ans.  water,  wood,  flannel.)  Tie  a  piece  of  iron  or  any 
metal  to  the  middle  of  a  strip  of  flannel,  2  or  3  ft.  long.  Press  the 
ends  of  the  flannel  in  your  ears,  and  if  the  metal  be  struck  against  iron, 
you  will  hear  a  sound  like  that  of  a  heavy  church  bell.  7.  How  is  the 
tremulous  motion  of  the  air  as  produced  by  a  sonorous  body  illustrated  .'' 
8.  What  is  said  of  the  velocity  of  sound  ?  9.  Ship  at  sea  ?  10.  Dis- 
tance of  lightning  ?  11 .  How  is  the  sound  of  an  echo  produced  ?  12. 
Describe  the  speaking  trumpet,  fig.  20. 

Note.  The  science  which  treats  of  sound  in  general  is  called 
acoustics. 


64  MUSICAL    SOUNDS 


LESSON  30. 

Nature  of  Musical  Sounds. 

Ten'sion,  act  of  stretching,  state  of  being  stretched. 

Grav'ity,  in  music,  the  moditicalion  of  any  sound,  by  which  it  be- 
comes deep  or  low  in  respect  of  some  other  sound. 

Con'cert,  many  performers  playing  the  same  tune. 

Line,  a  small  French  measure,  containing  the  12th  part  of  an  inch*. 
geometricians  conceive  the  line  subdivided  into  six  points. 

If  a  sonorous  body  be  struck  in  such  a  manner,  that  its 
vibrations  are  all  performed  in  regular  times,  the  vibrations 
of  the  air  will  correspond  with  them  ;  and  striking  in  the 
same  regular  manner  on  the  drum  of  the  ear,  will  produce 
the  same  uniform  sensation  on  the  auditory  nerve  and  ex- 
cite the  same  uniform  idea  in  the  mind  ;  or,  in  other  words, 
we  shall  hear  one  musical  tone.  But  if  the  vibrations  of  the 
sonorous  body  are  irregular,  there  will  necessarily  follow  a 
confusion  of  aerial  vibrations  ;  for  a  second  vibration  may 
commence  before  the  first  is  finished,  meet  it  half  way  on  its 
return,  intercept  it  in  its  course,  and  produce  harsh  jarring 
sounds  which  are  called  discords.  But  each  set  of  these 
irregular  vibrations,  if  repeated  at  equal  intervals,  would  pro- 
duce a  musical  tone.  It  is  only  their  irregular  succession 
which  makes  them  interfere,  and  occasions  discord. 

The  quicker  a  sonorous  body  vibrates,  the  more  acute,  or 
sharp  is  the  sound  produced  ;  and  the  vibrations  of  the  same 
string,  at  the  same  degree  of  tension,  are  always  of  a  similar 
duration.  Striking  the  note  in  quick  succession,  produces 
a  more  frequent  repetition  of  the  tone,  but  does  not  increase 
the  velocity  of  the  vibrations  of  the  string.  The  duration 
of  the  vibrations  of  the  strings  or  chords  depends  upon  their 
length,  their  thickness,  or  weight,  and  their  degree  of  ten- 
sion. The  difl'erent  length  and  size  of  the  strings  of  mu- 
sical instruments,  therefore,  serve  to  vary  the  duration  of  the 
vibrations,  and  consequently  the  acuteness  or  gravity  of  the 
notes. 

Among  the  variety  of  tones,  there  are  some  which,  sounded 
together,  please  the  ear,  producing  what  we  call  harmony  or 
concord.  This  arises  from  the  agreement  of  the  vibrations 
of  the  two  sonorous  bodies  ;  so  that  some  of  the  vibrations 
of  each  strike  upon  the  ear  at  the  same  time.     If  the  vibra- 


MUSICAL    BAROMETER  65 

tions  of  two  strings,  for  instance,  are  performed  in  equal 
ti'^ies,  the  same  tone  is  produced  by  both,  and  they  are  said 
to  be  in  unison.  But  concord  is  not  confined  to  unison ; 
for  two  different  tones  harmonize  in  a  variety  of  cases.  If 
one  string  or  sonorous  body  vibrates  in  double  the  time  of 
another,  the  second  vibration  of  the  latter  will  strike  upon 
the  ear  at  the  same  instant  as  the  first  vibration  of  the  for- 
mer ;  and  this  is  the  concord  of  an  eighth  or  octave.  If  the 
vibrations  of  two  strings  are  as  two  to  three,  the  second  vi- 
bration of  the  first  corresponds  with  the  third  vibration  of 
the  latter,  producing  the  harmony  called  a  fifth.  There  are 
other  tones  which,  though  they  cannot  be  struck  together 
without  producing  discord,  yet  if  struck  successively,  give 
us  the  pleasure  which  is  called  melody. 

A  sort  of  musical  barometer  has  been  invented  in  Swit- 
zerland, called  the  weather  harp,  which  possesses  the  sin- 
gular property  of  indicating  changes  of  the  weather  by  mu- 
sical tones.  In  the  year  1787,  one  was  constructed  in  the 
following  manner.  Thirteen  pieces  of  iron  wire,  each  three 
hundred  and  twenty  feet  long,  were  extended  across  a  garden, 
m  a  direction  parallel  to  the  meridian.  They  were  placed 
about  two  inches  apart ;  the  largest  were  two  lines.>M»dia- 
meter,  the  smallest  only  one,  and  the  others  one  and  a  half  j 
they  were  on  the  side  of  the  house,  and  made  an  aiwle  of* 
twenty  or  thirty  degrees  with  the  hprizon ;  -they  \v^S> 
stretched  and  kept  tight  by  wheels  made  for  that  purpose. 
Every  time  the  weather  changes,  these  wires  make  so  much- 
noise  that  it  is  impossible  to  continue  concerts  in  the  parlouj^ 
and  the  sound  resembles  that  of  a  tea-urn  when  boilipg,  and 
sometimes  that  of  a  distant  bell,  or  an  organ. 

QcjESTiONS. — 1.  When  do  the  vibrations  of  a  sonorous  body  pro- 
duce the  same  musical  tone  ?  2.  How  are  discords  produced  ?  3.  On 
what  does  the  sharpness  or  acuteness  of  a  musical  sound  depend  ?  4. 
On  what  does  the  duration  of  tlie  vibrations  of  strings  or  chords  dependji- 
5.  How  is  harmony  or  concord  produced  ?  6.  How  is  an  octave  con- 
cord produced  ?  7.  The  harmony  called  a  fifth  ?  8.  Describeithc 
musical  barometer  or  weather  harp.  [Note.  In  the  opinion  of -ace- 
lebrated  chemist,  this  is  an  electro-magnetical  phenomenon.]  9.  Illus- 
trate the  vibrations  of  a  musical  string  by  figures  17,  18j  and  19. 

6* 


OPTICS. 


LESSON  31. 


Optics. 

Lu'minous,  shining  by  its  own  light. 

Transpa'rent,  admitting  rays  of  light  to  pass  through. 

Opaque',  stopping  the  rays  of  light. 

Ze'nith,  a  point  in  the  heavens  directly  over  our  heads,  the  pole  of 
the  horizon.  Na'dir  is  a  point  diametrically  opposite  to  the 
zenith,  constituting  the  other  pole  of  the  horizon. 

Optics  is  the  science  which  treats  of  light,  and  of  the 
instruments  by  which  it  is  applied  to  useful  purposes.  It  is 
one  of  the  most  interesting  branches  of  natural  philosophy, 
but  not  one  of  the  easiest  to  understand ;  it  will  be  neces- 
sary, therefore,  that  you  give  to  it  the  whole  of  your  attention. 

Light,  when  emanated  from  the  sun,  or  any  other  lumi- 
nous body,  is  projected  forwards  in  straight  lines  in  every 
possible  direction  ;  so  that  the  luminous  body  is  not  only 
the  centre  from  whence  all  the  rays  proceed,  but  every  point 
of  it  may  be  considered  as  a  centre  which  radiates  light  in 
every  direction.  The  particles  of  light  are  so  extremely 
minute,  that  although  they  are  projected  in  difterent  direc- 
tions, and  cross  each  other,  yet  they  are  never  known  to  in- 
terfere, and  impede  each  other's  course.  It  is  still  a  disputed 
point,  however,  whether  light  be  a  substance  composed  of 
particles  like  other  bodies.  In  some  respects  it  is  obedient 
to  the  laws  which  govern  bodies  ;  in  others,  it  appears  to 
be  independent  of  them :  thus,  though  its  course  is  guid- 
ed by  the  laws  of  motion,  it  does  not  seem  to  be  influenced  by 
the  laws  of  gravity.  It  has  never  been  discovered  to  have 
weight,  though  a  variety  of  interesting  experiments  have 
been  made  with  a  view  of  ascertaining  that  point.  Some 
suppose  tliat  the  rays  of  light,  instead  of  being  particles^ 
consist  of  the  undulations  of  an  elastic  medium,  which  fills 
all  space,  and  which  produces  the  sensation  of  liglit  to  the 
eye,  just  as  tlie  vibrations  of  the  air  produce  X\\e  sensation 
of  sound  to  the  ear.  Most  of  the  plienomena  may  be  ac- 
counted for  by  either  hypothesis,  but  that  of  their  being  par- 
ticles applies  more  happily  to  some  of  the  facts  respecting 
the  modifications  of  light  by  refraction  and  reflection. 

When  rays  of  light  encounter  an  opaque  body,  part  of 
them  are  absorbed,  and  part  are  reflected,  and  rebound  just 


ItEFLECTION    OF   LIGHT.  67 

as  an  elastic  ball  which  is  struck  against  a  wall.  A  ray 
of  light  striking  perpendicularly  upon  a  plane  mirror,  is  re- 
flected back  in  the  same  direction  ;  but  those  rays  which 
strike  it  obliquely,  are  reflected  back  in  an  opposite  direction, 
but  with  the  same  obliquity ;  the  angle  of  reflection,  there- 
fore, is  exactly  equal  to  the  angle  of  incidence.  If  you  stand 
directly  before  a  looking-glass,  you  see  your  image  reflected 
back  to  you.  If  you  stand  a  little  to  the  side,  you  cannot 
see  yourself;  but  a  person  who  stands  just  as  far  on  the  other 
side  of  it,  can  see  your  image  in  the  glass,  and  you  can  see 
his.  If  you  place  a  candle  a  little  to  one  side,  you  must  go 
as  far  on  the  other  to  see  its  image  in  the  glass.  This  is  the 
same  rule  which  takes  place  in  the  collision  of  elastic  bodies 
against  any  surface.  If  you  strike  an  ivory  ball  or  common 
marble  perpendicularly  against  the  wainscot,  it  returns  to 
you ;  but  if  you  make  it  strike  sideways,  it  goes  off"  at  the 
same  angle  with  which  it  came  to  the  wainscot.  So  it  is 
with  rays  of  light ;  the  incident  ray,  or  the  ray  which  falls 
upon  a  surface,  makes  an  angle  with  a  perpendicular  line, 
drawn  from  the  point  where  it  strikes,  equal  to  that  which 
the  reflected  ray  makes  with  it. 

With  respect  to  a  looking-glass,  it  is  the  silvering  on  the 
glass  which  causes  the  reflection,  otherwise  the  rays  would 
pass  through  it  without  being  stopped,  and  if  they  were  not 
stopped  they  could  not  be  reflected.  No  glass,  however,  is 
so  transparent  but  it  reflects  some  rays :  if  you  put  your 
hand  near  a  window,  you  clearly  see  its  image  on  the  other 
side,  and  the  nearer  the  hand  is  to  the  glass,  the  more  evi- 
dent is  the  image.  Whatever  suffers  the  rays  of  light  to 
pass  through  it  is  called  a  medium,  and  the  more  transpa- 
rent the  body,  the  more  perfect  is  the  medium.  But  rays 
of  light  do  not  pass  through  a  transparent  medium,  (unless 
they  fall  perpendicularly  upon  it)  in  precisely  the  same  di- 
rection in  which  they  were  moving  before  they  entered  it. 
They  are  bent  out  of  their  former  course,  and  this  is  called 
refraction.  When  they  pass  out  of  a  rarer  into  a  denser 
medium,  as  from  air  into  water  or  glass,  they  are  always  re*- 
fracted  toward&  a  perpendicular  to  the  surface,  and  the  re* 
fraction  is,  more  or  less,  in  proportion  as  the  rays  fall,  more 
or  less,  obliquely  on  the  refracting  surface.  But  when  they 
pass  from  a  denser  into'  a  rarer  medium,  as  from  glass  or 
water  into  air,  they  move  in  a  direction  farther  from  the 


68  REFRACTION    OF    LIGHT, 

perpendicular.  If  you  put  a  piece  of  money  into  an  empty 
basin,  and  stand  at  such  a  distance  that  it  may  not  be  visi- 
ble ;  then  let  another  person  pour  water  into  the  basin,  and 
the  money  will  be  seen ;  for  the  rays  of  light,  in  passing 
from  a  denser  into  a  rarer  medium,  are  bent  froin  the  per- 
pendicular, and  thus  are  directed  to  your  eye.  The  follow- 
ing, therefore,  may  be  established  as  a  sort  of  axiom  in  op- 
tics :  we  see  every  thing  in  the  direction  of  that  line  in  which 
the  rays  approach  us  last.  If  you  place  a  candle  before  a 
looking-glass,  and  stand  before  it,  the  image  of  the  candle 
appears  behind  it ;  but  if  another  looking-glass  be  so  placed 
as  to  receive  the  reflected  rays  of  the  candle,  and  you  stand 
before  this  second  glass,  the  candle  will  appear  behind  that; 
because  the  mind  imagines  every  object  to  be  in  the  direc- 
tion from  which  the  rays  come  to  the  eye  last.  Hence,  when 
the  rays  of  light  coming  from  the  celestial  bodies,  arrive  at 
Qur  atmosphere,  they  are  bent  downward  ;  and  those  bodies 
appear,  when  in  the  horizon,  higher  than  they  are.  The 
effect  of  this  refraction  is  about  six  minutes  of  time,  but  the 
higher  they  rise,  the  less  are  the  rays  refracted  ;  and  when 
they  are  in  the  zenith,  they  suffer  no  refraction.  The  sun 
is  visible  about  three  minutes  before  he  rises,  and  about  the 
same  time  after  he  sets ;  making  in  the  course  of  a  year 
about  a  day  and  a  half  Twilight  is  occasioned  partly  by 
refraction,  but  chiefly  by  reflection  of  the  sun's  rays  by  the 
atmosphere,  and  it  lasts  till  tiic  oJn  is  eighteen  degrees  be- 
low the  horizon.  Were  there  no  atmosphere  to  reflect  and 
refract  the  sun's  rays,  only  that  part  of  the  heavens  would 
be  luminous  in  which  the  sun  is  placed  ;  and  if  we  could 
live  without  air,  and  should  turn  our  backs  to  the  sun,  the 
whole  heavens  would  appear  as  dark  as  in  the  night.  In 
this  case  also,  a  sudden  transition  from  the  brightest  sun- 
shine to  dark  night  would  immediately  take  place  upon  the 
setting  of  the  sun. 

Questions. — 1,  What  is  said  of  optics  ?  2.  In  what  manner  is 
light  projected  from  luminous  bodies  ?  3.  What  is  still  a  disputed 
point,  and  what  is  said  of  it  ?  4.  How  are  rays  of  light  reflected  ?  5. 
How  is  it  shown  that  the  angle  of  refleetionis  equal  to  the  angle  of 
incidence  ?  6.  What  is  raeant  by  the  refraction  of  rays  of  light  ?  7. 
How  are  they  refracted  in  passing  from  a  rarer  into  a  denser  medium  ? 
8.  From  a  denser  into  a  rarer  ?  9.  What  is  the  example  for  illustration  ? 
10.  What  may  be  established  as  a  sort  of  axiom  in  optics  ?  11.  Give 
the  illustration.    12.  What  is  the  effect  of  rays  of  light,  coming  from 


celestial  bodies,  being  refracted  by  the  atmosphere  r  13.  What  occa- 
sions twilight '  14.  How  would  the  heavens  appear  if  there  were  no 
atmosphere  ?  15.  Illustrate  the  reflection  of  light  by  fig.  29.  Engr.  III. 
16.  Refraction  of  light  by  fig.  29.  [Note.  Fig.  31.  is' a  vessel  with  a 
flower  in  water  at  the  bottom,  seen  by  the  eye  in  the  direction  of  the 
rays  which  enter  it.  This  experiment,  and  many  others,  may  be  easily 
performed.] 


LESSON  32. 

Different  hinds  of  Lenses. 

Diverge',  rays  of  light  coming  from  n point,  and  contmually  sepa- 
rating as  they  proceed,  are  said  to  diverge  ;  the  point  is  called 
the  radiant  point. 

Converge',  rays  which  tend  to  a  common  point  are  said  to 
coiiverge. 

A  Beam  of  light  is  a  body  of  parallel  rays;  xi  Pencil  of  rays  is  a 
body  of  diverging  or  converging  rays. 

Cam'era  obscu'ra,  a  chamber  darkened  ;  an  optical  machine  used 
in  a  darkened  chamber, 

A  LENS  is  a  glass  ground  into  such  a  form  as  to  collect  or 
disperse  the  rays  of  light  which  pass  through  it.  They  are 
of  different  shapes,  from  which  they  take  their  names.  If 
rays  proceed  from  a  radiant  point  distant  as  far  as  the  sun, 
their  divergency  is  so  trifling  that  they  may  be  considered  as 
parallel.  When  parallel  rays  fall  on  a  piece  of  glass  having 
a  double  convex  surface,  that  ray  only,  which  falls  in  the  di- 
rection of  the  axis  of  the  lens,  is  perpendicular  to  the  surface  , 
the  other  rays  falling  obliquely,  are  refracted  towards  the 
axis,  and  they  will  meet  beyond  the  lens  at  a  point  called  its 
focus.  The  distance  of  the  focus  from  the  centre  of  the  lens 
depends  both  upon  the  form  of  the  lens,  and  upon  the  re- 
fractive power  of  the  substance  of  which  it  is  made ;  in  a 
glass  lens,  both  sides  of  which  are  equally  convex,  the  focus 
is  situated  nearly  at  the  centre  of  the  sphere  of  which  the 
surface  of  the  lens  forms  a  portion  ;  it  is  at  the  distance, 
therefore,  of  half  the  diameter  of  the  sphere.  The  property 
of  a  lens  which  has  a  double  concave  surface  is  to  disperse 
the  rays  of  light.  Instead  of  converging  towards  the  ray, 
which  falls  on  the  axis  of  the  lens,  they  will  be  attracted 
towards  its  thick  edges,  both  on  entering  and  quitting  it, 
and  will,  therefore,  be  made  to  diverge.    Lenses  which  have 


IfO 


BURNING    GLASS; 


one  side  flat  and  the  other  convex  or  concave  are  less  povi''*  \ 
erful  in  their  refractions,  than  those  which  have  been  de-  1 
scribed.  They  are  called  plano-convex  and  plano-concave. 
The  focus  of  the  former  is  at  the  distance  of  the  diameter  ; 
of  a  sphere,  of  which  the  convex  surface  of  the  lens  forms  ' 
a  portion.  The  last  kind  of  lens  is  called  a  menis'cus,  being  j 
convex  on  one  side  and  concave  on  the  other,  like  the  glass  i 
or  crystal  of  a  watch. 

AH  the  parallel  rays  of  the  sun  which  pass  through  a , : 
convex  glass  are  collected  in  its  focus,  and  the  force  of  the  . 
heat  there  is  to  the  common  heat  of  the  sun,  as  the  surface  | 
of  the  glass  is  to  the  surface  of  the  focus.  If  a  lens  four 
inches  in  diameter  collect  the  sun's  rays  into  a  focus  at  the  J 
distance  of  twelve  inches,  the  image  will  not  be  more  than  ] 
one  tenth  of  an  inch  in  diameter  :  the  surface  of  this  little  < 
circle  is  one  thousand  six  hundred  times  less  than  the  surface  - 
of  the  lens,  and  consequently  the  heat  will  be  one  thousand  1 
six  hundred  times  greater  at  the  focus  than  at  the  lens.  A  ^ 
globular  decanter  of  water  acts  as  a  double  convex  lens,  and  I 
furniture  has  been  set  on  fire  by  leaving  one  incautiously  j 
exposed  to  the  rays  of  the  sun.  A  gentleman  of  London  ] 
formed  a  burning-glass  three  feet  in  diameter,  and  when  i 
fixed  in  its  frame,  it  exposed  a  clear  surface  of  more  than  ; 
two  feet  eight  inches  in  diameter,  and  its  focus,  by  means  ^ 
of  another  lens,  was  reduced  to  a  diameter  of  half  an  inch.  \ 
The  heat  produced  by  this  was  so  great  that  iron  plates  were  J 
melted  in  a  few  seconds  ;  tiles  and  slates  became  red-hot  in  ^^ 
a  moment,  and  were  vitrified,  or  changed  into  glass  ;  sulphur,  ; 
pitch,  and  other  resinous  bodies,  were  melted  under  water ;  I 
gold  was  rendered  fluid  in  a  few  seconds-  But  notwithstand-  1 
ing  this  intense  heat  at  the  focus,  the  finger  might,  without 
the  smallest  injury,  be  placed  in  the  cone  of  rays  within  an  ': 
inch  of  the  focus.  On  bringing  the  finger  nearer,  a  sensa-  *j 
tion  was  felt  like  that  produced  by  a  sharp  lancet,  and  not  ] 
at  all  similar  to  the  pain  occasioned  by  the  heat  of  fire  or  a  * 
candle.  Substances  of  a  white  colour  were  difficult  to  be  1 
acted  upon.  Pure  water  in  a  clear  glass  decanter  will  not  i 
be  warmed  by  the  most  powerful  lens,  but  a  piece  of  wood  * 
placed  in  the  water  may  be  burned  to  a  coal.  If  a  cavity  ; 
be  made  in  a  piece  of  charcoal,  and  the  substance  to  be 
acted  on  be  put  in  it,  the  effect  produced  by  the  lens  will  ; 
be  much  increased.     Any  metal  thus  enclosed  melts  in  a   j 


MIRRORS.  71 

moment :  the  fire  sparkling  like  that  of  a  forge  to  which  the 
blast  of  a  bellows  is  applied. 

The  image  of  an  object  when  received  through  a  convex 
lens  will  be  inverted.  If  you  cause  the  rays  of  light  from 
the  flame  of  a  candle  to  pass  through  the  glass  of  a  common 
spectacle,  and  receive  them  on  a  sheet  of  paper,  or  dark 
skreen  placed  at  a  proper  distance,  you  will  see  a  complete 
inverted  image  of  the  candle  on  it.  A  convex  lens  placed 
in  the  hole  of  a  window-shutter  will  exhibit,  on  a  white  sheet 
of  paper  situated  in  the  focus  of  the  glass,  all  the  objects  on 
the  outside,  as  fields,  trees,  men,  and  houses,  in  an  inverted 
order.  The  room  should  be  quite  dark,  and  the  sun  should 
shine  upon  the  objects.  A  portable  camera  obscura  may  be 
made  with  a  square  box,  in  one  side  of  which  is  to  be  fixed 
a  tube,  having  a  convex  lens  in  it :  within  the  box  is  a  plane 
mirror,  reclining  backwards  from  the  tube,  in  an  angle  of 
forty-five  degrees.  The  picture  is  formed  on  a  square  of  un- 
polished glass  at  the  top  of  the  box.  If  a  piece  of  oiled 
paper  be  stretched  on  the  glass,  a  landscape  may  be  easily 
copied  ;  or  the  outline  may  be  sketched  on  the  rough  surface 
of  the  glass. 

Questions. — 1.  What  is  a  Ions  ? — its  axis  ? — focus  ?  2.  Describe 
the  five  kinds  of  lenses.  3.  What  proportion  is  there  between  the 
common  heat  of  the  sun  and  the  heat  of  the  focus  of  a  double  convex 
lens  ?  4.  Describe  the  burning  glass  formed  at  London.  5.  What  ex- 
amples are  given  of  images  of  objects  being  inverted  by  a  convex  lens  .-' 
6.  How  may  a  camera  obscura  be  made  ?  7.  Why  is  the  mirror 
placed  at  an  angle  of  45  degrees  exactly  ?  Ans.  To  throw  the  image 
on  the  top,  for  incident  rays,  falling  upon  a  surface  declining  45  de- 
grees, will  be  reflected  at  an  equal  angle  of  45  degrees.  8.  Describo 
figures  30.  36.  32.  33. 


mm 


LESSON  33. 

3Iirrors. 


Panoram'ic,  exhibiting  a  succession  of  objects. 

Opti^cian,  a  maker  of  optical  instruments,  one  skilled  in  optics. 

Mirrors  are  made  of  glass,  silvered  on  one  side,  or  of 
some  metal  highly  polished.  There  are  three  kinds  of  them, 
the  plane,  the  convex,  and  tlie  concave.  Objects  seen  in 
convex  mirrors  are  diminished.     A  globe  of  glass,  silvered 


72  MIRRORS.  I 

on  the  inside,  is  sometimes  suspended  from  the  ceiling  of  a  " 
room.  It  affords  a  sort  of  panoramic  view  of  surrounding  \ 
objects,  though  not  ail  in  natural  proportion  of  size.  When  : 
a  convex  mirror  can  be  placed  before  a  window^,  either  with  i 
a  good  prospect,  or  where  there  are  a  number  of  persons^ 
passing  and  repassing  in  their  different  employments,  the  ^ 
images  reflected  from  it  will  be  erect,  and  behind  thei 
surface ;  and  a  landscape  or  a  busy  scene  delineated  on  one  ' 
of  them  is  always  a  beautiful  object  to  the  eye.  Concaved 
mirrors  make  objects  appear  larger,  but  distorted.  If  one  be  ' 
hung  on  the  wall  of  a  room,  or  fixed  in  a  chair,  a  person  be- j 
yond  the  focus  sees  his  image  inverted.  As  he  puts  forward  f 
his  hand  the  image  in  the  glass  appears  to  do  the  same,  as  j 
if  to  shake  hands.  As  he  tries  to  clasp  the  hand  it  vanishes' 
from  his  view.  Let  the  spectator  hold  out  a  knife  in  hia-' 
hand,  the  image  will  appear  to  do  the  same  ;  and  so  strong  ; 
will  be  the  impression  on  his  mind,  that  he  will  feel  a  reluc-  l 
tance  to  run  his  hand  forward  against  the  apparent  weapon.  ) 
A  concave  mirror  throws  back  the  sun's  rays  into  one  point  ^ 
or  focus,  where  paper  or  gunpowder  may  be  set  on  fire.  ] 
Mirrors  are  sometimes  made  of  a  cylindrical  concave  form  , 
and  as  one  of  them  is  placed  either  upright  or  on  its  side,  1 
the  image  of  the  picture  is  distorted  into  a  very  long  or  a  I 
very  broad  image.  Reflecting  surfaces  may  be  made  of  i 
various  shapes,  and  if  a  regular  figure  be  placed  before  an  ^ 
irregular  reflector,  the  image  will  be  deformed ;  but  if  an  .^ 
object,  as  a  picture,  be  painted  deformed,  according  to  cer-  i 
tain  rules,  the  image  will  appear  regular.  Such  figures  and  | 
reflectors  are  sold  by  opticians,  and  they  serve  to  astonish  | 
those  who  are  ignorant  of  these  subjects.  i 

Small  convex  reflectors  are  made  for  the  use  of  travellers,  -] 
who,  when  fatigued  by  stretching  the  eye  to  Alps  towering 
on  Alps,  can   by  their  mirror,   bring  these  sublime  objects 
into  a  narrow  compass,   and  gratify  the  sight  by  pictures  i 
which  the  art  of  man  in  vain  attempts  to  imitate.  ] 

Questions. — 1.  What  are  the  three  kinds  of  mirrors?  2.  How 
do  convex  mirrors  make  objects  appear  ? — concave  ?  3.  What  are  1 
.some  of  the  experiments  that  may  be  performed  with  them  ?  4.  How  \ 
do  cylindrical  concave  mirrors  make  an  image  of  a  picture  appear?  l 
[Note.  A  mirror  is  sometimes  called  a  Spoc'ulum,  pi.  Spec'ala.]  5.  1 
Describe  fig.  27, 


COLOURS.  78 


LESSON  34. 


Colours. 

Sem'icircle,  a  half  round,  part  of  a  circle  divided  by  the  diameter, 
Juncture,  the  line  at  which  two  things  are  joined  together. 
Prism,  a  solid  piece  of  glass  with  three  flat  sides,  and  two  equal 
and  parallel  triangular  ends. 

Sir  Isaac  Newton,  to  whom  we  are  indebted  for  the  most 
important  discoveries  respecting  light  and  colours,  was  the 
first  who  divided  a  white  ray  of  light,  and  found  it  to  con- 
sist of  an  assemblage  of  coloured  rays.  This  separation 
may  be  observed  in  the  well  known  experiment  of  the  prism. 
A  ray  being  let  into  a  darkened  room,  through  a  small  round 
aperture  in  the  shutter,  and  falling  on  a  triangular  glass 
prism,  is,  by  the  refraction  of  the  prism,  considerably  dilat- 
ed, and  it  will  exhibit,  on  a  skreen  or  on  the  opposite  wall, 
an  oblong  image  called  a  spectrum,  variously  coloured ;  the 
extremities  of  which  are  bounded  by  semicircles,  and  the 
sides  are  rectilinear.  The  colours  are  commonly  divided 
into  seven,  which,  however,  have  various  shades  gradually 
intermixing  at  their  juncture.  The  following  lines  from 
Blackmore  represent  their  order,  beginning  at  the  side  of  the 
refracting  angle  of  the  prism. 

Of  parent  colours,  first  the  flaming  red 
Sprung  vivid  forth  ;  the  tawny  orange,  next ; 
And  next,  delicious  yellow ;  by  whose  side 
Fell  the  kind  beams  of  all-refreshing  green; 
Then  the  pure  blue,  that  swells  autumnal  skies, 
Ethereal  played  ;  and  then,  of  sadder  hue, 
Emerged  tfie  deepened  indigo,  as  when 
The  heavy  skirted  evening  droops  with  frost, 
Whilethe  last  gleamings  of  refracted  light 
Died  in  the  fainting  violet  away. 
The  union  of  these  colours,  in  the  proportions  in  which 
they  appear  in  the  spectrum,  produce  in  us  the  idea  of 
whiteness.     If  you  paint  a  card  in  compartments  with  these 
seven  colours,  and  whirl  it  rapidly  on  a  pin,  it  will  appear 
white.     But  a  more  decided  proof  of  the  composition  of  a 
white  ray  is  afforded  by  uniting  these  coloured  rays,  and 
forming  with  them  a  ray  of  white  light.     This  can  be  done 
7 


74 


THE    PRISM. 


by  letting  the  coloured  rays,  which  have  been  separated  by  a    ^ 

prism,  fall  upon  a  lens,  which  will  converge  them  to  a  focus,    ) 

and,  being  thus  re-united,  will  appear  white  as  they  did  before    ] 

refraction.  ] 

Prisms  are  commonly  made  of  solid  glass,  but  those  who  i 

do  not  possess  one  of  this  kind  may  easily  make  a  substitute.   -^ 

Take  three  pieces  of  plate  glass,  each  four  or  six  inches    ; 

long,  and  two  or  three  inches  wide  :  procure  a  tin  frame,  i 

the  two  ends  of  which  are  in  the  exact  shape  of  the  three    j 

pieces  of  glass  placed  in  the  form  of  a  triangle,  with  a  strip   j 

of  tin  running  from  each  angle  of  one  end  to  the  angles  or  | 

corners  of  the  other.     These  strips  are  bent  so  as  to  receive  | 

the  two  edges  of  the  glass  plates.     The  tin  forming  the  ends  | 

is  turned  up  so  as  to  receive  tlie  plates,  and  one  of  the  ends  \ 

is  furnished  with  a  little  tube  to  pour  in  water.     When  the  | 

frame  and  the  glass  plates  are  fastened  together,  and  the  ere-  1 

vices  stopped,  the  prism  is  filled  with  clear  water,  and  is  \ 

ready  for  experiment.  I 

When  a  spectrum  is  formed  by  the  light  which  has  pass-  j 

ed  through  a  prism  upon  a  skreen,  if  a  small  hole  be  made  \ 

through  the  skreen,  and  the  rays  of  one  colour  only  be  per-  J 

mitted  to  pass  through  it,  then  whatever  is  viewed  in  that  \ 

light,  will  appear  of  that  particular  colour.     Thus  if  red  1 

light  only  has  passed  through  the  hole,  then  blood,  or  grass,  j 

or  milk,  viewed  in  tha*  light  behind  the  skreen,  will  appear  • 

red  ;  excepting  that  the  blood  will  appear  of  a  stronger  red  .^ 

colour  than  the  grass  or  milk.     If  the  blue  light  only  has| 

been  transmitted  through  the   hole,  then  the  above  men-  | 

tioned  substances  will  appear  blue  ;  and  the  like  must  be  j 

understood  of  the   other  colours.      This   proves   that  the  \ 

colours,  which  seem  to  proceed  from  coloured  bodies  in  ge-  \ 

neral,  do  not  belong  to  those  bodies ;  but  they  are  the  com-  \ 

ponent  parts  of  the  white  light,  in  which  those  bodies  are  ? 

viewed,  and  that  certain  bodies  have  the  property  of  absorb-  \ 

ing  some  of  those  coloured  rays  of  the  white  light  which  ^ 

falls  upon  them,  and  of  reflecting  others.     Thus,  grass  re-  - 

fleets  the  green  rays  and  absorbs  the  rest ;  hence,  the  green  J 

rays  coming  to  our  eyes,  render  the   uppearaTice  of  grass  , 

green  ;  thus  blood  absorbs  every  other  coloured  ray  except-  \ 

ing  the  red,  and  so  forth.     Black  bodies  absorb  all  the  seven^^ 

coloured  rays,  and  white  bodies  reflect  them  all.    Providence  ^ 

appears  to  have  decorated  nature  with  the  enchanting  di-  , 


THE    RAINBOW.  "J^ 

Versity  of  colours  which  we  so  much  admire,  for  the  purpose 
of  beautifying  the  scene,  and  rendering  it  a  source  of  plea- 
sureable  enjoyment.  It  is  an  ornament  which  embellishes 
nature  wherever  we  behold  her. 

Questions. — 1.  Of  what  was  Sir  Isaac  Newton  the  first  disco- 
verer ?  2.  How  may  a  white  ray  of  light  be  separated  into  the  va- 
rious colours  of  which  it  is  composed  ?  3.  How  arc  the  colours 
divided,  and  what  are  they  called  -*  4.  How  is  the  idea,  of  whiteness 
produced  ? — What  is  the  proof  of  this  .''  5.  How  may  a  substitute 
lor  a  solid  glass  prism  be  made  ?  6.  How  is  it  proved  that  the  colours 
which  seem  to  proceed  from  coloured  bodies  do  not  belong  to  those 
bodies  .'  7.  What  are  colours  .'  8.  Wliat  is  a  spectrum  ?  9.  Describe 
fig.  37. 


LESSON  35. 

JVie  Rainhoio,  Halo,  and  Parhelia. 

Parhe'lia,  (singular,  Parhe'lion)  a  bright  light  appearing  on  o»e 
side  of  the  sun. 

When  the  rays  of  tlie  sun  strike  upon  drops  of  water  fall- 
ing from  the  clouds,  and  we  are  placed  in  such  a  direction 
that  our  back  is  towards  the  sun,  and  the  clouds  before  us, 
we  observe  a  peculiar  phenomenon  in  the  heavens,  called  a 
rainbow.  We  may  consider  the  drops  of  rain  as  transparent 
globules  upon  which  the  rays  fall,  and  are  twice  refracted 
and  once  reflected.  Hence  proceed  the  different  colours  of 
the  rainbow.  These  colours  appear  the  more  vivid,  as  the 
clouds  which  are  behind  are  darker,  and  the  drops  of  rain 
fall  closer.  The  drops  continually  forming  produce  a  nevB^ 
rainbow  every  moment,  and  as  each  spectator  observes  it 
from  a  particular  situation,  it  happens  that  scarcely  two  men, 
strictly  speaking,  see  the  same  rainbow  ;  and  this  appear 
ance  can  only  last  whilst  the  drops  which  fall  are  succeeded 
by  others. 

Triumphal  arch,  that  fdl'st  the  sky 
When  storms  prepare  to  part,' 

I  ask  not  proud  philosophy 
To  teach  me  what  thou  art — 

Still  seen,  as  to  my  childhood's  sight, 

A  midway  station  given 
For  happy  spirits  to  alight 

Betwixt  the  earth  and  heaven. 


76  THE    RAINBOW. 

Can  all  that  optics  teach,  unfold 
Thy  form  to  please  me  so, 

As  when  I  dreamt  of  gems  and  gold 
Hid  in  thy  radiant  bow. 

When  Science  from  Creation's  face 
Enchantment's  veil  withdraws 

What  lovely  visions  yield  their  place 
To  cold  material  laws. 

And  yet,  fair  bow,  no  fabling  dreams, 
But  words  of  the  Most  High, 

Have  told  why  first  thy  robe  of  beams 
Was  woven  in  the  sky. 

When  o'er  the  green  undeluged  earth 
Heaven's  covenant  thou  didst  shine, 

How  came  the  world's  grey  fathers  forth 
To  watch  thy  sacred  sign  ! 

And  when  its  yellow  lustre  smiled 
O'er  mountains  yet  untrod. 

Each  mother  held  aloft  her  child 
To  bless  the  bow  of  God. 

Methinks  thy  jubilee  to  keep, 
The  first-made  anthem,  rang 

On  earth  delivered  from  the  deep, 
And  the  first  poet  sang. 

Nor  ever  shall  the  Muse's  eye 
Unraptured  greet  thy  beam  : 

Theme  of  primeval  prophecy, 
Be  still  the  poet's  theme  ! 

The  earth  to  thee  her  incense  yields, 
The  lark  thy  welcome  sings, 

When  glittering  in  the  freshen'd  fields 
The  snowy  mushroom  springs. 

How  glorious  is  thy  girdle  cast 
O'er  mountain,  tower,  and  town, 

Or  mirror'd  in  the  ocean  vast, 
A  thousand  fathoms  down. 


HALO   AND    PARHELIA.  77 

As  fresh  in  yon  horizon  dark^ 

As  young  thy  beauties  seem, 
As  when  the  eagle  from  the  ark 

First  sported  in  thy  beam. 

For  faithful  to  its  sacred  page, 

Heaven  still  rebuilds  thy  span, 
Nor  lets  the  type  grow  pale  with  age, 

That  first  spoke  peace  to  man. 

Campbell. 

In  serene  weather,  we  often  observe  a  circular  light,  or 
luminous  ring  surrounding  the  moon  ;  it  is  called  a  halo, 
or  crown.  Its  outline  sometimes  faintly  shows  the  colours 
of  the  rainbow.  The  moon  is  in  the  middle  of  this  ring, 
and  the  intermediate  space  is  generally  darker  than  the  rest 
of  the  sky.  When  the  moon  is  at  the  full,  and  consider- 
ably elevated  above  the  horizon,  the  ring  appears  most  lu- 
minous. It  is  often  very  large.  We  are  not  right  in  sup- 
posing, that  this  circle  really  surrounds  the  moon  ;  the  true 
cause  of  such  an  appearance  must  be  looked  for  in  our  at- 
mosphere, the  vapours  of  which  make  a  refraction  of  the 
rays  of  light.  False  moons  are  sometimes  seen  near  the  real 
moon,  and  appear  as  large,  but  their  light  is  paler.  They 
are  generally  accompanied  by  circles,  some  of  which  have 
the  same  colours  as  the  rainbow,  whilst  others  are  white, 
and  others  have  long  luminous  tails.  All  these  appearances 
are  produced  by  refraction.  The  rays  of  light  falling  from 
the  moon  upon  aqueous  and  sometimes  frozen  vapours,  are 
refracted  in  various  ways ;  the  coloured  rays  are  separated, 
and  reaching  the  eye  present  a  new  image  of  the  moon. 

Parhelia  or  mock-suns  are  far  more  rarely  seen,  but  their 
appearance  is  wonderfully  curious.  They  generally  appear 
about  the  size  of  the  true  sun,  not  quite  so  bright,  though  they 
are  said  sometimes  to  rival  their  parent  luminary  in  splen- 
dour. When  there  are  a  number  of  them  they  are  not  equal 
to  each  other  in  brightness.  Externally,  they  are  tinged 
with  colours  like  the  rainbow.  They  are  not  always  round, 
and  have  sometimes  a  long  fiery  tail  opposite  the  sun,  but 
are  paler  towards  the  extremity.  They  are  formed  by  the 
reflection  of  the  sun's  beams  on  a  cloud. 

Questions. — 1.    Under  what  circumstances  do  we  perceive  the 
rainbow  ?    2.  What  ie  a  halo  ?    3   What  are  parhelia,  or  raock-8U»s 
7» 


78  THE    EYE. 


LESSON  36. 

Structure  of  the  Eye. 

Mem'branous,  consisting  of  a  web  of  several  sorts  of  fibres  inter- 
woven together. 

Op'tic,  producing  vision,  subservient  to  vision. 

Sclerot'ica,  (pronounced  skle-rot'-i-ca,)  derived  from  a  Greek  word 
signifying  hard. 

The  body  of  tlie  eye  is  of  a  spherical  form.  It  has  two 
membranous  coverings  ;  the  external  one  is  called  the  scle- 
rotica ;  this  has  a  projection  in  that  part  of  the  eye  which 
is  exposed  to  view,  called  the  cornea,  because,  when  dried, 
it  has  nearly  the  consistence  of  very  tine  horn,  and  is  suffi- 
ciently transparent  for  the  light  to  obtain  free  passage  through 
it.  The  second  membrane,  which  lines  the  cornea,  and  en- 
velopes the  eye,  is  called  the  choroid;  this  has  an  opening 
in  front  just  beneath  the  cornea,  which  forms  the  pupil, 
through  which  the  rays,  of  light  pass  into  the  eye.  The 
pupil  is  surrounded  by  a  circular  border,  M'hich  is  a  part  of 
the  choroid  and  called  the  iris,  composed  of  a  sort  of  net- 
work, which  contracts  or  expands  according  to  the  force  of 
the  light  in  which  it  is  placed.  If  a  person  sits  looking 
towards  a  window,  the  pupils  of  his  eyes  appear  very  small, 
and  the  iris  large.  When  he  turns  from  the  window,  and 
covers  his  eyes  with  his  hands,  so  as  entirely  to  exclude  tlie 
light  for  a  few  moments,  the  pupils  will  be  enlarged  and  the 
iris  diminished.  Tliis  is  the  reason  vyhy  the  eyes  suffer  pain^ 
when  from  darkness  they  suddenly  come  into  a  strong  light ; 
for  the  pupil  being  dilated,  a  quantity  of  rays  must  rush  in 
before  it  has  time  to  contract.  And  when  we  go  from  a 
strong  light  into  obscurity,  we  at  first  imagine  ourselves  in  total 
darkness  ;  for  a  sufficient  number  of  rays  cannot  gain  ad- 
mittance into  the  contracted  pupil  to  enable  us  to  distin- 
guish objects  :  but  in  a  few  minutes  it  dilates,  and  we  clearly 
perceive  objects  which  were  before  invisible. 

The  choroid  is  imbued  with  a  black  liquor  which  serves 
to  absorb  all  the  rays  that  are  irregularly  reflected,  and  to 
convert  the  body  of  the  eye  into  a  more  perfect  camera  ob- 
scura.  Y/itliin  these  coverings  of  the  eye-ball  are  contained 
three  transparent  substances,  called  humours.  Tlie  first 
©ecupies  the  space  immediately  behind  the  cornea,  and  is 


THE    EYE.  70 

called  the  aqueous  humour,  from  its  liquidity  and  resem- 
blance to  water.  Beyond  this  is  situated  the  crystalline 
humour,  so  called  fram  its  clearness  and  transparency  ;  it 
has  the  form  of  a  lens,  and  refracts  the  rays  of  light  in  a 
greater  degree  of  perfection  than  any  that  have  been  con- 
structed by  art.  The  back  part  of  the  eye,  between  the 
crystalline  humour  and  the  retina,  is  filled  by  the  vitreous 
humour,  which  derives  its  name  from  its  supposed  resem- 
blance to  glass.  The  most  important  part  of  the  eye  is  the 
retina ;  for  it  is  that  which  receives  the  impression  of  the 
objects  of  sight,  and  conveys  it  to  the  mind.  It  consists  of 
an  expansion  of  the  optic  nerve  of  the  most  perfect  AVhite- 
ness  :  it  proceeds  from  the  brain,  enters  the  eye  and  is  finally 
spread  over  the  interior  surface  of  the  choroid.  The  refrac- 
tion occasioned  by  the  several  humours  unites  the  v.'hole  of 
a  pencil  of  rays,  proceeding  from  any  one  point  of  an  object, 
to  a  corresponding  point  on  the  retina,  and  the  image  is  thus 
rendered  distinct  and  strong.  Tlie  muscles  of  the  eye  are 
six,  and  by  the  excellence  of  their  arrangement  it  is  enabled 
to  move  in  all  directions. 

All  three  of  the  humours  of  the  eye  have  some  effect  in 
refracting  the  rays  of  light,  but  the  crystalline  is  the  most 
powerful  :  it  is  a  complete  double  convex  lens  ;  and  as  every 
point  of  an  object  sends  out  rays  in  all  directions,  some 
rays  from  each  point  on  the  side  next  the  eye  will  be  con- 
verged and  brought  to  as  many  points  on  the  retina,  and  will 
form  on  it  a  distinct  inverted  picture  of  the  object,  which  is 
seen  erect  by  the  habit  of  the  mind.  Although  an  image 
must  be  formed  on  the  retina  of  each  of  our  eyes,  yet  we 
do  not  see  objects  double  ;  for  when  an  object  is  seen  dis- 
tinctly with  both  eyes,  the  axis  of  each  is  directed  to  it,  and 
the  object  appears  single  ;  but  if  the  axes  of  both  eyes  are 
not  directed  to  the  object,  it  always  appears  double.  If  you 
look  at  any  object,  and  then  by  pressing  upon  the  under  or 
upper  side  of  one  eye,  remove  it  out  of  its  natural  place,  you 
will  see  two  objects,  whose  distance  from  each  other  will 
vary  as  the  eye  is  more  or  less  turned  from  its  natural 
position. 

It  is  well  known  that  an  object  at  a  distance  appears 
smaller  than  when  it  is  near.  The  reason  is,  that  the  nearer 
any  object  can  be  brought  to  the  eye,  the  larger  will  be  the 
angle  under  which  it  appears  ;  for  the  rays  fall  more  diver* 


80  THE    EYE. 


gent  upon  the  crystalline  humour,  and  consequently  includej 
a  greater  angle,  and  thus  the  object  is  magnified.  In  objects 
placed  at  such  distances  as  we  are  used  to,  we  know,  by, 
experience,  how  much  an  increase  of  distance  will  diminish^ 
their  apparent  magnitude,  and  we  instantly  suppose  them  of| 
the  size  they  would  appear  if  they  were  less  remote ;  but^ 
this  can  only  be  done,  where  we  are  well  acquainted  withi 
the  real  magnitude  of  the  object ;  in  all  other  cases  w® 
judge  of  magnitudes  by  the  angle  under  which  the  object 
appears  at  tlie  known,  or  supposed  distance  ;  that  is,  we  infer 
the  real  magnitude  from  the  apparent  magnitude  in  compari-j 
son  with  the  distance  of  the  object.  Sight,  therefore,  does  no^ 
represent  extension  such  as  it  is  in  itself;  it  often  deceiveai 
us  both  in  regard  to  the  size  and  the  distance  of  objectsj," 
and  we  should  be  led  into  continual  errors  if  experience  di(| 
not  set  us  fight.  This  is  rendered  strikingly  manifest^ 
from  the  case  of  a  young  man  who  was  blind  fiom  his  mri 
fancy,  and  who  recovered  his  sight  at  the  age  of  fourteen,^ 
by  the  operation  of  couching.  At  first  he  had  no  idea  either' 
of  the  size  or  distance  of  objects,  but  imagined  that  uvery^ 
thing  he  saw  touched  his  eyes ;  and  it  was  not  till  aften 
having  repeatedly  felt  them  and  walked  from  one  object  toj 
another,  that  he  acquired  an  idea  of  their  respective  dimen-*! 
sions,  their  relative  situations,  and  their  distances. 

Questions. — 1.  What  is  the  external  covering  of  the  eye  called .'—, 
Describe  it.  2.  Describe  the  cornea.  3.  The  choroid.  4.  The  pupil.  51 
The  iris.  6.  What  is  said  in  order  to  illustrate  the  contraction  and  dila«^ 
tation  of  the  iris  .^  7.  Of  what  use  is  the  black  liquor  in  the  choroid  .'j 
8.  Describe  the  three  humours  of  the  aye.  9.  Of  what  does  the  retfna! 
consist,  and  what  is  its  use  ?  10.  How  is  the  image  on  the  retina  ren- 1 
dered  distinct  ?  11.  How  does  it  appear  that  the  image  on  the  retina- 
will  be  inverted  ?  12.  Having  two  eyes,  why  do  we  not  see  objects^ 
double  ^  13.  Why  does  a  distant  object  appear  smaller  than  one  that] 
is  near  ?  14.  How  do  we  judge  of  the  real  magnitudes  of  objects  ;\ 
15.  What  case  is  related  to  show  that  experience  is  necessary  to  correct"; 
the  errors  of  sight  ?  IG.  Look  at  fig.  28.  and  describe  the  eye.j 
[Note.  Let  the  instructor  explain  to  his  pupils  how  objects  of  equals 
magnitudes  appear  under  a  greater  angle  when  near,  than  when  at  aj 
distance.}  I 


SPECTACLES.  81 


LESSON  37. 

Optical  Instruments. 

Land'scape,  the  prospect  of  a  country, — also  a  picture  represent- 
ing an  extent  of  space  with  the  various  objects  on  it. 

Glob'ule,  a  small  particle  of  matter  of  a  globular  or  spherical 
figure. 

As  the  sight  is  the  most  noble  and  extensive  of  all  our 
senses;  as  we  make  the  most  frequent  use  of  our  eyes  in 
all  the  actions  and  concerns  of  life  ;  that  instrument  which 
relieves  the  eyes  when  decayed,  and  supplies  their  defects, 
must  be  estimated  as  one  of  the  greatest  of  advantages. 
Sight  may  be  defective  in  various  ways.  Some  eyes  are  too 
flat,  others  are  too  convex  or  round ;  in  some,  the  humours 
lose  a  part  of  their  transparency,  and  on  that  account,  much 
of  the  light  that  enters  the  eye  is  stopped  and  lost  in  the 
passage,  and  every  object  appears  dim.  Spectacles  are  in- 
tended to  collect  the  light  and  to  bring  it  to  a  proper  degree 
of  convergency.  The  honour  of  their  invention  was  claimed 
by  Salvinus  Armatus,  a  nobleman  of  Florence,  who  died 
in  1317,  and  the  fact  was  inscribed  on  his  tomb.  When  the 
eye  is  too  flat,  the  rays  proceeding  from  objects  do  not  con- 
verge to  a  focus  so  soon  as  they  reach  the  retina ;  in  this 
case  a  convex  glass  is  necessary,  for  it  has  the  property  of 
converging  the  rays,  and  of  course,  when  suited  to  the  eye, 
ef  bringing  them  to  a  focus,  and  forming  an  image  on  the 
retina.  When  the  eye  is  too  convex,  the  rays  of  light  are 
converged  to  a  focus  before  they  reach  the  retina  ;  to  remedy 
this,  a  concave  glass  is  used,  which  causes  the  rays  to  di- 
verge, and  prevents  their  coming  to  a  focus  too  soon.  Short- 
sighted persons  bring  objects  close  to  their  eyes ;  it  has  a 
similar  effect  to  that  produced  by  concave  glasses  ;  for  the 
nearer  an  object  is  brought  to  the  eye,  the  greater  is  the 
angle  under  which  it  is  seen,  that  is,  the  extreme  rays,  and 
of  course  all  the  others,  are  made  more  divergent.  But  per- 
sons whose  eyes  are  too  flat,  when  examining  an  object,  hold 
it  at  a  distance,  for  the  farther  an  object  is  held  from  their 
eyes,  the  less  is  the  divergency  of  its  rays,  that  is,  the  smaller 
is  the  angle  under  which  it  is  seen  :  the  focal  distance  is  in- 
creased, and  an  image  is  properly  formed  on  the  retina.  In  con- 
sidering vision  as  achieved  by  the  means  of  an  image  formed 


82  MICROSCOPES.  « 

at  the  bottom  of  the  eye,  we  can  never  reflect,  without  wort-* 
der,  upon  the  smalhiess,  yet  correctness  of  the  picture,  the 
subtilty  of  the  touch,  the  fineness  of  the  lines.  A  land- 
scape of  five  or  six  square  leagues  is  brought  into  a  space 
of  half  an  inch  diameter ;  yet  the  multitude  of  objects 
which  it  contains  are  all  preserved ;  are  all  discriminated  id 
their  magnitudes,  positions,  figures,  colours. 

Microscopes  are  instruments  for  viewing  small  objects ; 
and  they  apparently  magnify  them,  because  they  enable  us 
to  see  them  nearer  than  with  the  naked  eye,  without  affect- 
ing the  distinctness  of  vision.  The  distance  from  the  naked 
eye,  at  which  most  persons  are  supposed  to  see  small  objects 
best,  is  about  seven  inches  ;  but  by  the  help  of  convex  glasses, 
we  are  enabled  to  view  things  clearly  at  a  much  shorter  dis- 
tance  than  this  ;  for  the  nature  of  a  convex  lens  is,  to  render 
an  object  distinctly  visible  to  the  eye  at  the  distance  of  it| 
focus.  With  a  knowledge  of  this  fact,  we  may  easily  de^ 
termine  the  magnifying  powers  of  glasses  employed  in  Sin-^ 
glc  Microscopes,  which  are  small  double  convex  lensesj 
having  the  object  placed  in  the  focus,  and  the  eye  at  thq 
same  distance  on  the  other  side.  If  rays  of  light  from  aioi 
object  are  converged  to  a  point  at  the  distance  of  one  inctj 
from  the  centre  of  the  glass,  or,  in  other  words,  if  the  focali 
distance  of  the  lens  is  one  inch,  an  object  may  be  seert 
through  that  lens  at  one  inch  distance  from  the  eye,  and  i| 
will  appear,  in  its  diameter, — since  the  natural  sight  is  seve^ 
inches, — seven  times  larger  than  to  the  naked  eye.  But 
the  object  is  magnified  every  way  equally,  in  length  as  we 
as  breadth,  we  must  square  this  diameter,  to  know  real! 
how  much  the  object  appears  enlarged ;  and  we  shall  thu» 
find  that  its  surface  is  magnified  forty-nine  times.  If  wfls 
suppose  the  focus  of  a  convex  lens  to  be  at  one-tenth  of  ang 
inch  distant  from  its  centre,  in  seven  inches  there  arc^ 
seventy  such  tenths  of  an  inch  ;  and  an  object  therefore  maj^ 
be  seen  through  this  lens  seventy  times  nearer  than  it  canjl 
distinctly,  by  the  naked  eye.  It  will  consequently  appeal^ 
seventy  times  longer  and  seventy  times  broader  than  it  doe* 
to  common  sight;  and  as  seventy  multiplied  by  seventyfj 
makes  four  thousand  nine  hundred  ;  so  many  times  it  really^ 
appears  magnified.  Those  lenses,  therefore,  which  have  thej 
shortest  focus,  will  magnify  the  object  most.  Single  micro-^ 
scopes  of  the  greatest  power  may  be  made  with  a  very  small! 


I 


Microscopic  discoveries.  83 

globule  of  glass,  fixed  in  a  thin  plate  of  metal,  so  that  the 
middle  of  it  may  be  directly  over  the  centre  of  an  extremely 
small  hole  made  in  the  plate. 

The  compound  microscope  consists  of  at  least  two  lenses, 
by  one  of  which  an  image  is  formed  within  the  tube  of  the 
microscope  ;  and  this  image  is  viewed  through  the  eye-glass, 
instead  of  the  object  itself.  The  solar  microscope  is  a  kind 
of  camera  obscura,  which,  in  a  darkened  chamber,  throws 
the  image  on  a  wall  or  skreen.  It  consists  of  two  lenses 
fixed  opposite  to  a  hole  in  a  board  or  window-shutter.  There 
is  also  a  plane  reflector  or  mirror  placed  without,  which  may 
be  so  regulated  as  to  throw  the  sun's  rays  upon  the  outer 
Jens".  A  magic  lantern  is  constructed  on  the  same  prm- 
ciples.  The  light  is  supplied  by  a  lamp  instead  of  the  sun, 
and  it  is  used  for  magnifying  paintings  on  glass,  and  throw- 
ing their  images  upon  a  white  skreen  in  a  darkened  chamber. 

Questions. — 1.  In  what  ways  may  sight  be  defective  .'  2.  For 
what  are  spectacles  intended  ?  3.  How  do  they  assist  eyes  that  are 
too  flat  ?  4.  Too  convex  or  round  ?  5.  Why  do  some  persons  bring 
objects  close  to  tiieir  eyes,  and  others  hold  them  at  a  distance  ?  6. 
What  are  microscopep  ^  7.  Sin^^le  microscopes  ?  8.  How  is  their 
magnifying  power  calculated  ?  9.  Describe  the  compound  microscope. 
10.  Solar  microscope.  11.  Magic  lantern.  12.  Look  on  fig.  35.  and 
describe  the  single  microscope.  13.  On  fig.  34.  and  describe  the  com- 
pound microscope. 


LESSON  38. 

Microscopic  Discoveries. 

Miniature,  (pronounced  min'e-ture,)  representation  in  a  small 

compass.     Fil'ament,  a  slender  thread. 
Ped'icle,  a  footstalk.     Animal'cule,  a  small  animal. 
Con'ical,  consisting  of  a  circular  base  or  bottom  and  ending  in  a 

point. 
Tissue,  (pron.  tish'Q,)   a  substance   interwoven  with  threads,  or 

va-riegatcd. 

Tjje  microscope  has  opened  to  us  a  new  world  of  insects 
and  Vegetables ;  it  has  taught  us  that  objects,  invisible  to  the 
naked  eye,  exist,  having  figure,  extension,  and  different 
parts  ;  some  examples  of  which  we  shall  produce,  that  we 
may  have  more  reasons  for  admiring  and  praising  the  wis- 
dom and  power  of  God.  A  grain  of  sand  when  examined 
Dy  the  eye  appears  round,   but  with  the  help  of  a  glass  we 


84  MICROSCOPIC    DISCOVERIES.  j 

observe  that  each  grain  differs  from  the  other,  both  in  size  ' 
and  figure  ;  some  of  them  are  perfectly  round,  others  square,  i 
some  conica],  and  the  greater  part  of  an  irregular  form.  By 
microscopes  which  magnify  objects  millions  of  times,  we  ^ 
can  discover  in  the  grains  of  sand  a  new  animal  world  ;  for  J 
within  their  cavity  dwell  various  insects.  In  the  vegetable  j 
kingdom  we  are  presented  with  a  thick  forest  of  trees  and  ' 
plants,  bearing  leaves,  branches,  flowers,  and  fruits.  Mouldi-  ; 
ness,  when  looked  at  by  the  naked  eye,  seems  nothing  but  J 
an  irregular  tissue  of  filaments ;  but  the  magnifying  glass 
shows  it  to  be  a  forest  of  small  plants,  which  derive  their  i 
nourishment  from  the  moist  substance  which  serves  them  , 
as  a  base.  The  stems  of  these  plants  may  be  plainly  distin-  j 
guished,  and  sometimes  their  buds,  some  shut  and  some.i 
open.  They  have  much  similarity  to  mushrooms,  which,  \ 
it  is  well  known,  are  the  growth  of  a  single  night ;  but  ^ 
those  in  miniature,  of  which  we  are  speaking,  seem  to  come  \ 
to  perfection  in  a  much  less  space  of  time  ;  hence  we  account  ; 
for  the  extraordinary  progress  which  mouldiness  makes  in  a  \ 
few  hours.  A  sort  of  dust,  which  covers  some  stones,  has  J 
been  found  to  consist  of  small  mushrooms,  raised  on  pedicles,  \ 
the  heads  of  which,  round  the  middle,  were  turned  up  at  the  \ 
edges.  Above  their  covering  a  multitude  of  small  grains  ap- 
pear, shaped  like  cherries  somewhat  flattened ;  and  among  \ 
them  several  small  red  insects,  which  probably  feed  upon  them.  ^ 
A  small  drop  of  ^e  green  surface  of  water,  that  has  stood  ] 
for  some  time,  has  been  found  to  be  altogether  composed  of  i 
animalcules  of  several  shapes  and  magnitudes.  The  mostj 
remarkable  were  those  that  gave  the  water  the  green  colour ;  j 
they  were  oval  creatures ;  they  could  contract  and  dilate 
themselves,  tumble  over  many  times  together,  and  then  shoot  i 
away  like  fishes.  \ 

If  you  slightly  bruise  some  corns  of  pepper,  and  infuse  j 
them  in  water  for  a  few  days,  and  then  expose  a  drop  of  it  to  i 
the  microscope,  a  number  of  animalcules  will  be  visible,  in  ' 
continual  motion,  going  backwards  and  forwards  in  all  di-  \ 
rections,  turning  aside  when  they  meet  each  other,  or  when  j 
their  passage  is  stopped  by  some  obstacle.  In  other  infu-  \ 
sions,  as  in  that  of  new  liay,  differently  shaped  animalcules  : 
will  be  found.  When  the  drop  in  which  they  swim,  and  : 
which  to  them  is  like  a  pond,  becomes  diminished  by  evapo-  \ 
ration,  they  gradually  retire  towards  the  middle,  where  they  j 


MICROSCOPIC    DISCOVERIES,  85 

accumulate,  and  at  length,  when  entirely  deprived  of  moist- 
ure, perish.  Previously  to  this  they  appear  in  great  distress, 
writhe  their  bodies,  and  endeavour  to  escape  from  that  state 
of  uneasiness  which  they  evidently  feel.  If  the  smallest 
quantity  of  sulphuric  acid  be  put  into  a  drop  of  the  infusion 
which  swarms  with  these  insects,  they  immediately  throw 
themselves  on  their  backs  and  expire. 

Upon  examining  the  edge  of  a  very  sharp  lancet  with  a 
microscope,  it  will  appear  as  broad  as  the  back  of  a  knife  ; 
rough,  uneven,  full  of  notches  and  furrows.  An  exceed- 
ingly small  needle  resembles  a  rough  iron  bar.  But  the 
sting  of  a  bee,  seen  though  the  same  instrument,  exhibits 
every  where  a  most  beautiful  polish,  without  the  least  flaw, 
blemish,  or  inequality,  and  it  ends  in  a  point  too  fine  to  be 
discerned.  The  threads  of  fine  lawn  seem  coarser  than  the 
yarn  with  which  ropes  are  made  for  anchors.  But  a  silk- 
Worm's  web  appears  perfectly  smooth  and  shining,  and  every 
where  equal.  The  smallest  dot,  that  can  be  made  with  a 
pen,  appears  irregular  and  uneven.  But  the  little  specks  on 
the  wings  or  bodies  of  insects  are  found  to  be  most  accu- 
rately circular.  The  finest  miniature  paintings  appear  be- 
fore the  microscope  rugged  and  uneven,  entirely  void  of 
beauty,  either  in  the  drawing  or  colouring.  The  most  even 
and  beautiful  varnishes  will  be  found  to  be  mere  roughness. 
But  the  nearer  we  examine  the  works  of  God,  even  in  the 
least  of  his  productions,  the  more  sensible  shall  we  be  of  his 
wisdom  and  power.  In  the  numberless  species  of  insects, 
what  proportion,  exactness,  uniformity,  and  symmetry  do  we 
perceive  in  all  their  organs  !  what  a  profusion  of  colouring  ! 
azure,  green,  and  vermilion,  gold,  silver,  pearls,  rubies,  and 
diamonds ;  fringe  and  embroidery  on  their  bodies,  wmgs, 
heads,  and  every  other  part !  how  high  the  finishing,  how 
inimitable  the  polish  we  every  where  behold  ! 

On  the  gay  bosom  of  some  fragrant  flower 
They,  idly  fluttering,  live  their  little  hour ; 
Their  life  all  pleasure,  and  their  task  all  play, 
All  spring  their  age,  and  sunshine  all  their  day. 
Not  so  the  child  of  sorrow,  wretched  man, 
His  course  with  toil  concludes,  with  pain  began ; 
That  his  high  destiny  he  might  discern. 
And  in  misfortune's  school  this  lesson  learn  ; 
8 


66  THE    TELESCOPE.  1 

Pleasure  's  the  portion  of  th'  inferior  kind, 
But  glory,  virtue,  Heaven  for  man  designed.  ; 

Barbauld. 

Questions. — 1.  What  has  the  microscope  done  for  us  ?  2.  What  '^ 
is  the  appearance  of  grains  of  sand  when  examined  by  the  eye,  and  ■ 
by  the  microscope'  3.  Mouldiness  ?  4.  What  is  said  of  the  green  j 
surface  of  standing  water  ?  5.  What  is  the  appearance  of  animalcules  ] 
in  the  infusions  of  pepper  ? — now  hay  ?  G.  What  appearance  has  the  : 
edge  of  a  lancet  ?  7.  Sting  of  a  bee  ?  8.  Fine  lawn  ?  9.  Silk  worm's  j 
web  ?  1 


LESSON  39.  3 

I 
The  Telescope  and  Telegraph.  4 

Satellite,  a  small  planet  revolving  round  a  larger,  a  moon.  i 

Octag'onal,  having  eight  angles  and  sides.  i 

O'ral,  delivered  verbally,  not  written.  ; 

No  invention  in  the  mechanic  arts  has  ever  proved  more  i 
useful  and  entertaining  than  the  production  of  the  telescope  ;-] 
its  utility  both  by  sea  and  land  is  too  well  known  to  need  3 
observation  ;  and  without  such  assistance  the  science  of  as- 1 
tronomy  must  have  been  far  short  of  its  present  state.  A 
telescope  is  useful,  not  only  for  discovering  tliose  distantj 
objects  that  are  invisible  to  the  naked  eye,  but  for  rendering  j 
more  clear  and  distinct  those  that  are  discernible  ;  it  is  con-  3 
structed  to  act  either  by  refraction  or  reflection.  It  is  the  j 
sole  business  of  all  telescopes  to. enable  the  eye  to  see  thes^ 
object  under  a  larger  angle.  For  this  purpose  a  new  image  of^ 
an  object  is  produced  by  the  object-glass  of  the  telescope,  and  i 
then  this  image  is  viewed  by  means  of  the  eye-glasses.  Th©^;; 
first  impression,  conveyed  to  the  mind  by  a  telescope,  is  that  * 
of  bringing  the  object  nearer,  which  is  only  another  mode -J 
of  declaring  that  it  is  enlarged,  or  seen  under  a  larger  angle,  j 
To  show  objects  in  their  natural  posture,  a  telescope  must  ; 
have  three  eye-glasses.  The  two  additional  lenses  simply  ] 
give  an  erect  position  to  objects.  If  you  remove  one  of  the  J 
eye-glasses  from  a  common  telescope,  every  thing  wdl  appear ' 
in  an  inverted  position.  The  three  eye-glasses  have  all  theif  j 
focal  distances  equal,  and  the  magnifying  power  is  found  by  | 
dividing  the  focal  distance  of  the  object-glass  by  the  focal  ; 
distance  of  one  of  the  eye-glasses.     The  two  additional  lenses  j 


THE   TELEGRAPH.  B^^ 

are  not  necessary  for  astronomical  telescopes ;  for  no  incon- 
venience arises  from  seeing  the  celestial  bodies  inverted. 

When  very  great  magnifying  power  is  required,  telescopes 
are  constructed  with  concave  mirrors,  and  called  reflecting 
telescopes.  Mirrors  are  used  in  order  to  bring  the  image 
nearer  the  eye  ;  and  a  lens  or  eye-glass  is  for  the  same  pur- 
pose as  in  the  refracting  telescope,  that  is,  to  magnify  the 
image.  The  Newtonian  reflecting  telescope  consists  of  a 
tube,  towards  the  end  of  which  a  concave  mirror  is  placed. 
The  reflected  converging  rays,  before  they  reach  the  focus, 
are  made  to  fall  upon  a  plane  mirror  placed  at  an  angle  of 
forty-five  degrees,  and  thus  are  thrown  upwards  to  the  focus 
of  a  convex  lens  fixed  in  the  upper  side  of  the  telescope, 
through  which  the  eye  looks  down  on  the  image.  In  the 
telescopes  made  by  Dr.  Herschel  there  is  but  one  mirror, 
which  is  placed  at  the  lower  end  of  the  tube,  with  such 
an  inclination,  that  the  rays  are  brought  to  a  focus  and  the 
image  formed  near  the  edge  of  the  upper  end  of  the  tube. 
The  image,  therefore,  is  formed  by  only  one  rcjiection,  and  its 
brightness,  when  viewed  through  the  lens  is,  on  this  account, 
greater  than  that  in  the  Newtonian  telescope.  The  head 
of  the  observer,  when  a  large  aperture  is  wanted,  may  be 
placed  entirely  at  one  edge  of  the  tube,  so  as  not  to  intercept 
any  of  the  rays  at  the  time  of  making  an  observation ;  but 
as  the  eye  looks  down  the  tube,  the  back  must  be  turned  to 
the  object.  Dr.  Herschel's  grand  telescope  is  nearly  forty 
feet  long,  and  four  feet  ten  inches  in  diameter.  The  con- 
cave polished  surface  of  the  great  mirror  is  forty-eight  inches 
in  diameter,  and  it  magnifies  six  thousand  times.  This  noble 
instrument  was,  in  all  its  parts,  constructed  under  the  sole 
direction  of  Dr.  Herschel  :  it  was  begun  in  the  year  1785, 
and  completed  August  28th,  1789,  on  which  day  was  dis- 
covered the  sixth  satellite  of  Saturn. 

The  telegraph  is  a  machine  for  communicating  intelli- 
gence at  a  considerable  distance,  by  making  various  signals, 
— which  have  been  previously  agreed  upon  between  two 
parties, — to  represent  letters,  words,  or  ideas.  No  machine 
for  making  signals  can  with  propriety  be  called  a  telegraph, 
unless  it  is  adapted  to  express  a  suflicient  number  of  letters 
or  words  to  form  a  complete  language,  and  which  can  be 
made,  therefore,  to  communicate  any  information  which  can 
be  expressed  by  oral  or  written  language.     Less  perfect  sys- 


88  ASTRONOMY.  'i 

i 
i 

terns  of  signals  which  extend  only  so  far  as  to  communicate  j 
intelligence  of  events  which  have  been  foreseen,  and  the  | 
appropriate  signals,  previously  arranged,  are  called  signal  ] 
flags,  signal  lanterns,  and  signal  guns  or  fires.  Telegraphs  ] 
have  been  constructed  in  various  ways.  What  is  called  the  ] 
English  telegraph  consists  of  six  octagonal  boards,  each  of  ] 
which  is  poised  upon  an  axis  in  a  frame,  and  worked  by  : 
means  of  ropes  in  the  manner  of  bell-ropes,  so  that  it  can  ; 
either  be  placed  vertically,  and  appear  with  its  full  size  to  ^ 
the  observer  at  the  nearest  station,  or  it  becomes  invisible  to  j 
him  by  being  placed  horizontally,  so  that  the  narrow  edge  j 
alone  is  exposed,  which  from  a  distance  cannot  be  seen.  | 
Six  boards  make  thirty-six  changes,  by  the  most  plain  and  | 
simple  mode  of  working ;  and  they  will  make  many  more,  if  | 
more  were  necessary ;  but  as  the  real  superiority  of  the  te-  ^ 
legraph,  over  all  other  modes  of  making  signals,  consists  in  'j 
its  making  letters,  it  is  not  necessary  that  the  changes  should  j 
be  more  than  the  letters  of  the  alphabet,  and  the  arithme-  J 
tical  figures.  Telegraphs  of  this  description  are  set  up  on  1 
eminences  at  the  distance  of  eight,  ten,  or  twelve  miles  ;  | 
and  a  line  of  them,  by  repeating  each  other's  signals,  conrj 
veys  a  message  at  the  rate  of  a  hundred  miles  in  about  five  j 
minutes.  A  telescope  for  the  use  of  the  observer  is  fixed ^ 
in  the  watch-tower  of  each  station.  "I 

Questions. — 1.  Of  what  advantage  is  the  telescope  ?  2.  Why  does  I 
it  seem  to  bring  an  object  nearer  ?  ^.  What  is  said  of  the  eye-glasses M 
and  the  magnifying  power  of  telescopes  ?  4.  Why  are  mirrors  usedj 
in  reflecting  telescopes  ?  5.  Describe  the  Newtonian  telescope.  6.| 
Describe  the  telescope  as  made  by  Dr.  Herschel.  7.  His  grand  tele- 1 
scope.  8.  What  is  a  telegraph.^  9.  How  is  a  proper  telegraph  dis-' 
tinguished  from  other  machines  for  making  signals  ?  10.  Describe »; 
the  English  telegraph.  11.  What  is  said  of  its  number  of  changes  ?^ 
12.  At  what  rate  will  such  telegraphs  convey  a  message  ?  13.  How  | 
may  an  idea  of  the  Newtonian  telescope  be  obtained  by  looking  at  ^ 
fig.  27.  1 


LESSON  40.  - 

I 
Astronomy.  - 

Locomo'tive,  having  the  power  of  removing,  or  changing  place.  .'^ 

Astronomy  is  the  science  which  teaches  the  magnitudes^ 

and  motions,  distances,  periods,  and  order  of  the  celestia.l| 


ASTRONOMY.  89 

bodies.  It  is  the  boldest  and  most  comprehensive  of  all  our 
speculations.  It  is  the  science  of  the  material  universe  con- 
sidered as  a  whole.  The  wide-spreading  firmament,  while 
it  lifts  itself  above  all  mortal  things,  exhibits  to  us  that  lu- 
minary, which  is  the  light,  and  life,  and  glory  of  our  world, 
and  when  this  retires  from  our  view,  is  lighted  up  with  a 
thousand  lesser  fires,  that  never  cease  to  burn,  that  never 
fail  to  take  their  accustomed  places,  and  never  rest  from 
their  slow,  solemn,  and  noiseless  march.  Among  the  objects 
more  immediately  about  us,  all  is  vicissitude  and  change. 
Plants  arise  out  of  the  earth,  flourish  awhile  and  decay,  and 
their  place  is  filled  by  others.  Animals  also  have  their  pe- 
riods of  growth  and  decline.  Even  man  is  not  exempt  from 
the  general  law.  Nations  are  like  individuals,  privileged 
only  with  a  more  protracted  existence.  The  firm  earth  itself, 
the  theatre  of  all  this  change,  partakes  in  a  degree  of  the 
common  lot  of  its  inhabitants,  and  the  sea  once  heaved  its 
waves  where  now  rolls  a  tide  of  wealth  and  population.  Situ- 
ated as  we  are,  in  this  fleeting,  fluctuating  state,  it  is  consol- 
ing to  be  able  to  dwell  upon  an  enduring  scene,  to  contem- 
plate laws  that  are  immutable,  an  order  that  has  never  been, 
interrupted,  to  fix,  not  the  thoughts  only,  but  the  eye,  upon 
ol>jects  that  after  the  lapse  of  so  many  ages,  and  the  fall  of 
so  many  states,  cities,  human  institutions,  and  monuments  of 
art,  continue  to  occupy  the  same  places,  to  move  with  the 
same  regularity,  and  to  shine  with  the  same  pure,  fresh,  un- 
diminished lustre. 

Astronomy  is  the  most  improved  of  all  the  branches  of 
knowledge,  and  that  which  does  the  greatest  credit  to  the 
human  understanding.  We  have  in  this  obtained  the  object 
of  our  researches.  We  have  solved  the  great  problem  pro- 
posed to  us  in  the  celestial  motions  ;  and  our  solution  is  as 
simple  and  as  grand  as  the  spectacle  itself,  and  is  in  every 
respect  worthy  of  so  exalted  a  subject.  It  is  not  the  as- 
tronomer only,  who  is  thus  satisfied,  but  the  proof  is  of  a 
nature  to  carry  conviction  to  the  most  illiterate  and  skep- 
tical. Our  knowledge,  extending  to  the  principles  and  laws 
which  the  author  of  nature  has  chosen  to  impress  upon  his 
works,  comprehends  the  future ;  it  resembles  that  which  has 
been  regarded  as  the  exclusive  attribute  of  supreme  intelli- 
gence. We  are  thus  enabled,  not  only  to  explain  those  unu- 
sual appeafances  in  the  heavens,  which  were  formerly  the 
8* 


90  ASTRONOMY.  ^ 

occasion  of  such  unworthy  fears,  but  to  forewarn  men  o^j 
their  occurrence ;  and  by  predicting  the  time,  place,  and  ■ 
circumstances  of  the  phenomenon,  to  disarm  it  of  its  terror.  \ 

There  is,  however,  nothing  perhaps  so  surprising  in  this 
science,  as  that  it  makes  us  acquainted  with  methods,  by^ 
which  we  can  survey  those  bright  fields  on  which  it  is  em-y 
ployed,  and  apply  our  own  familiar  measures  to  the  pathsl 
which  are  there  traced,  and  to  the  bodies  that  trace  them  ;  ; 
that  we  can  estimate  the  form,  and  dimensions,  and  inequa-  ] 
lities  of  objects  so  immense,  and  so  far  removed  from  the  ; 
little  scene  of  our  labours.  What  would  be  the  astonish- 
ment of  an  inhabitant  of  one  of  those  bodies,  of  Jupiter  for  ] 
instance,  to  find  that,  by  means  of  instruments  of  a  few  feet| 
in  length,  and  certain  figures  and  characters  still  smaller,  = 
all  of  our  own  invention,  we  had  succeeded  in  determining^ 
the  magnitude  and  weight  of  this  great  planet,  the  length  of  i 
its  days  and  nights,  and  the  variety  of  its  seasons,  that  we  had  J 
watched  the  motions  of  its  moons,  calculated  their  eclipses,  and  ■ 
applied  them  to  important  domestic  purposes  ?  What  would  >; 
be  our  astonishment  to  learn,  that  an  insect,  one  of  those  for  \ 
instance  which  serve  sometimes  to  illuminate  the  waters  of  \ 
the  ocean,  though  confined  by  the  exercise  of  its  proper  j 
organs  and  locomotive  powers,  to  the  sphere  of  a  few  inches,  | 
had,  by  artificial  aids  of  its  own  contriving,  been  able  to  i 
extend  its  sphere  of  observation  to  the  huge  monsters  that  ; 
move  about  it ;  that  it  had  even  attempted,  not  altogether  '■ 
without  success,  to  fathom  the  depth  of  the  abyss,  in  which  ^ 
it  occupies  so  insignificant  a  place,  and  to  number  the  beings  ' 
it  contains  ?  ^ 

The  first  use  of  the  telescope,  about  the  commencement  j 
of  the  seventeenth  century,  opened  a  new  and  most  brilliant  | 
era  in  the  science  of  astronomy.     The  defect  of  the  natural  | 
organ  with  respect  to  the  objects  of  this  science  had  never  ; 
been  recognised.     We  had  gazed  upon  them  without  com-  - 
prehending  what  we  saw.     We  had  cast  a  vacant  eye  over 
the  splendid  pages  of  this  volume,  as  children  amuse  them- 
selves with  a  book  which  they  are  unable  to  read.     We  had 
caught  here  and  there  a  capital  letter,  or  a  picture,  but  we 
had  failed  to  distinguish  those  smaller  characters  on  which  the 
sense  of  the  whole  depended.     It  is  not  the  least  of  the  ad- 
vantages of  this  wonderful  instrument,  that  it  has  taught  us 
the  importance  of  those  means  of  improvement  and  enjoy- 


THE    SOLAR   SYSTEM.  91 

meht,  which  are  placed  within  the  reach  of  our  own  inge- 
nuity and  skill.  No  one  surely  would  have  dreamed  of  pro- 
curing such  an  aid  to  the  natural  sight,  any  more  than  of 
creating  a  new  sense.  It  would  have  seemed  like  changing 
the  law  of  our  being,  and  the  condition  in  which  we  are 
placed.  We  have,  by  means  of  this  instrument,  emerged,  as 
it  were,  from  a  prison.  The  mind  has  effected  its  enlarge- 
ment, as  an  insect  bursts  its  little  tenement,  and  flutters 
through  the  free  air,  and  over  the  gay  fields. 

Another  change  in  this  science,  of  the  first  importance, 
was  wrought  by  the  genius  of  Kepler,  who  died  in  the  year 
1630.  But  the  last  and  most  important  of  all  the  revolutions 
that  have  taken  place  in  it,  is  that  achieved  by  Newton. 
There  is  no  other  instance  of  so  signal  a  change  in  the  opi- 
nions and  pursuits  of  the  philosophic  world.  It  may  be  com- 
pared to  those  great  and  rapid  conquests,  by  which  new 
boundaries  and  new  laws  have  been  given  to  states  and  king- 
doms, and  new  directions  to  the  industry  and  active  employ- 
ments of  men ;  with  this  difference,  however,  that  these 
have  been  made  by  violence,  and  with  the  aid  and  co-opera- 
tion of  others,  while  the  revolution  in  the  sciences  effected 
by  Newton,  was  the  silent,  solitary  work  of  an  individual. 

Questions. — 1,  What  is  astronomy  ?  2.  What  is  said  of  the  im- 
proved slate  of  this  brancli  of  knowledge  ?  3.  What  may  be  regard- 
ed as  most  surprising  in  it  ?  4.  What  is  said  of  the  first  use  and  im- 
portance of  the  telescope  ?  5.  What  is  said  of  Kepler  ?  6.  Of  Newton  ? 
[Note.  Nev\i;on  died  March  1727,  aged  85.] 


LESSON  41. 

The  Solar  St/ stem. 

Or' bit,  the  path  in  which  a  celestial  body  moves. 
Car'dinal,  one  of  the  chief  officers  in  the  church  of  Rome. 
Inquisi'tion,  a  court  established  for  the  detection  of  heresj-. 

The  true  solar  system  consists  of  the  sun  and  an  unknown 
number  of  opaque  bodies,  which  revolve  round  the  sun,  and 
some  of  which  at  the  same  time  revolve  round  others. 
Those  which  revolve  round  the  sun  only,  are  called  primary 
planets  and  comets.  Those  which  revolve  round  a  primary 
planet,  at  the  same  time  they  are  revolving  round  the  sun, 


92*  GALILEO. 

are  called  secondary  planets,  moons,  or  satellites.  The 
number  of  comets  is  unknown.  The  sun  is  the  centre  of 
the  system,  and  the  eleven  primary  planets,  at  different  dis- 
tances, and  in  different  times,  move  round  him,  from  west  to 
east,  in  the  following  order,  Mercury,  Venus,  the  Earth, 
Mars,  Vesta,  Juno,  Pallas,  Ceres,  Jupiter,  Saturn,  and  Her- 
schel  or  Uranus.  The  Earth  has  one  moon,  Jupiter  four, 
Saturn  seven,  and  Uranus  six.  Venus  and  Mercury  being 
nearer  to  the  sun  than  our  earth,  are  called  inferior  planets, 
and  all  the  rest,  which  are  without  the  earth's  orbit,  are 
(failed  5Mpenor  planets;  some  astronomers  distinguish  them  by 
the  terms  interior  and  exterior,  which  seem  preferable.  The 
planets  are  retained  in  their  orbits  by  the  united  operation  of 
the  centripetal  force,  by  which  a  body  is  attracted  to  the 
centre  of  gravity,  and  the  centrifugal  force,  by  which  it  en- 
deavours to  persevere  in  a  straight  line.  These  two  powers, 
mutually  balancing  each  other,  compel  them  to  make  their 
respective  revolutions.  The  time  of  performing  their  revo- 
lutions round  the  sun  is  called  their  year,  and  the  time  of 
performing  their  revolution  on  their  axis,  their  day.  The 
axis  of  a  planet  is  an  imaginary  line  conceived  to  be  drawn 
through  its  centre,  about  which  it  revolves,  and  the  extremi- 
ties of  this  line,  terminating  on  opposite  points  of  the  planet's 
surface,  are  called  \is  poles. 

The  first  material  step  in  improving  the  science  of  astro- 
nomy was  the  establishment  of  the  present  arrangement  of 
the  sun  and  planets  by  Copernicus,  who  died  in  the  year 
1543.  This  doctrine,  it  is  true,  was  held  by  Pythag'oras, 
but  it  was  now  presented  in  a  new  and  stronger  light,  with 
its  leading  features  more  fully  and  distinctly  unfolded.  It 
is  remarkable,  that  in  so  many  instances,  it  should  have  ex- 
posed its  authors  and  defenders  to  persecution.  Pythagoras, 
we  are  told,  made  it  known  only  to  a  select  few  ;  but  one  of 
his  disciples,  who  had  the  courage  to  teach  it  publicly,,  was 
obliged  to  flee  in  order  to  escape  the  odium  it  excited. 
Copernicus  meditated  upon  the  subject  for  many  years,  be- 
fore he  undertook  to  give  his  thoughts  to  the  world,  and 
scarcely  surviving  the  publication  of  his  work,  he  left  to 
others  to  receive  the  shock  that  awaited  those  who  espoused 
it.  Galileo  could  not  resist  the  accumulated  evidence,  that 
presented  itself  to  his  enlarged  and  philosophic  mind,  in 
iavour  of  this  refined  scheme,  and  was  accordingly  destined 


THE    SUN.  9^ 

to  bear  the  whole  weight  of  indignation  that  was  ready  to 
burst  upon  the  disturbers  of  a  prejudice  so  old  and  so  deeply 
rooted.  He  was  arrested,  and  seven  cardinals  clothed  with 
the  authority  of  the  church  sat  in  judgment  upon  him,  and 
sentenced  him  to  the  prison  of  the  Inquisition  for  opinions, 
which  they  pronounced  false  in  philosophy,  heretical,  and 
contrary  to  the  word  of  God.  After  a  year's  confinement  he 
was  liberated,  but  continuing  his  discoveries,  and  apparently 
persevering  in  his  opinions,  he  was  imprisoned  a  second 
time.  After  being  made  to  abjure  what  were  deemed  his 
errors,  and  to  do  penance  for  his  offences,  he  was  again  re- 
stored to  liberty.  Indignant  at  the  cruelty  of  this  treatment, 
and  the  bigotry  and  blindness  of  his  persecutors,  he  yet 
continued  his  pursuits  ;  but  in  silence  and  fear.  His  ex- 
cessive application,  and  the  constant  use  of  his  telescope, 
together  with  frequent  exposure  to  the  air  by  night,  had  such 
an  effect  upon  him,  that  he  lost  his  sight.  He  died  in  1642, 
at  the  age  of  seventy-eight. 

Questions. — 1.  Of  what  does  the  solar  system  consist  ?  2.  Wi^t 
are  primary  planets  ? — secondary  planets  ?  3.  What  is  the  order  in 
which  the  eleven  primary  planets  move  round  the  sim  ?  4.  What 
planets  have  moons,  and  how  many  have  each  ?  5.  What  are  interior 
and  exterior  planets  ?  6.  How  are  the  planets  retained  in  their  orbits? 
7.  Define  year,  day,  axis,  poles.  8.  What  was  the  first  material  step 
in  the  progress  of  astronomy  .'  9.  What  is  remarkable  with  respect 
to  the  true  doctrine  of  the  solar  system  ?  10.  What  course  did  Coper- 
nicus adopt?     11.  What  is  said  of  Galileo?     12.  Explain  Engr.  IV. 


LESSON  42. 


The  Sun. 


Spher'oid,  a  body  approaching  to  the  form  of  a  sphere,  but  not 
exactly  round. 

EIHp'tical,  oval, — an  ellipse  is  produced  from  the  section  of  a 
cone  by  a  plane  cutting  both  its  sides,  but  not  parallel  to  the 
base.  All  the  planets  move  round  the  sun  in  elliptical  orbits, 
and  the  sun  itself  is  situated  in  one  of  the  foci  of  each  ellipse  : 
that  focus  is  called  the  lower  focus.  See  the  Earth's  orbit  in 
fig.  40. 

Great  source  of  day  !  best  image  here  below 

Of  thy  Creator,  ever  pouring  wide, 

From  world  to  world,  the  vital  ocean  round ; 


94                                                         THE    SUN.  I 

On  nature,  write  with  every  beam,  His  praise. 

Soul  of  surrounding  worlds  ! —  i 

'Tis  by  thy  secret,  strong,  attractive  force,  1 

As  with  a  chain  indissolubly  bound,  .; 

Thy  system  rolls  entire  ;  far  from  the  bourn  j 

Of  utmost  Herschcl,  wheeling  wide  his  round  i 

Oi  eighty  years  ;  to  Mercury  whose  disk  \ 

Can  scarce  be  caught  by  philosophic  eye,  \ 

Lost  in  the  near  effulgence  of  thy  blaze.     Thomson.  j 

The  sun  is  a  fountain  of  light  that  illuminates  the  world ;  | 
it  is  the  cause  of  that  heat  which  maintains  the  productive  '  j 
power  of  nature,  and  makes  the  earth  a  fit  habitation  for  i 
man.     The  figure  of  the  sun  is  a  spheroid,  higher  under  the  •  \ 
equator  than  about  the  poles  ;  and  his  diameter  is  computed  \ 
to  be  nearly  nine  hundred  thousand  miles.     His  solid  bulk  \ 
is  more  than  a  million  of  times  larger  than  that  of  the  earth.  1 
The  sun  has  two  motions ;  the  one  is  a  periodical  motion,  in 
an  elliptical  or  very  nearly  circular  direction,  round  the  com-  ' 
rrtbn  centre  of  all  the  planetary  motions  ;  the  other  is  a  revo-  '■ 
lution  upon  its  axis,  which  is  completed  in  about  twenty-six  ' 
days.     That  the  sun  has  a  rotation  round  his  axis  is  made  1 
evident   by  the  spots  seen  on  his   surface.     Some   of  these 
spots  have  made  their  first  appearance  near  the  edge  or  \ 
margin  of  the  sun,  and  have  been  seen  some  time  after  on  ; 
the  opposite  edge ;  whence,  after  a  stay  of  more  than  thir- 
teen days,   they  have  re-appeared  in  their  first  place,  and  ; 
taken  the  same  course  over  again.     These  spots  were  en-  | 
tirely  unknown  before  the  invention  of  telescopes,  though  " 
they  are  sometimes  of  sufficient  magnitude  to  be  discerned  , 
by  the  naked  eye.     Some  have  been  so  large,  as  by  compu-  ; 
tation  to  be*capable  of  covering  the  continents  of  Asia  and 
Africa,  the  whole  surface  of  the  earth,  or  even  five  times 
its  surface.     The   sun   has  commonly   been  considered  a 
globe  of  fire  ;  but  this  has  been  doubted  by  modern  astrono- 
mers.    The  celebrated  Herschel  considers  the  sun  as  a  most 
magnificent  hahitable  globe,  surrounded  by  a  very  extensive  ' 
atmosphere,  which  consists  of  elastic  fluids  that  are  more  or 
less  lucid  and  transparent ;  and  of  which  the  lucid  ones  fur- 
nish us  with  light.     The  appearances,   called  spots  in  the 
sun,  he  considers  as  real  openings  in  the  luminous  clouds  i 
of  the  solar  atmosphere.       •  | 


MERCUHY.  95 

The  sun  is  accompanied  by  a  phenomenon  called  the  zo- 
diacal light.  It  is  a  beam  of  light  of  a  triangular  form,  visi- 
ble a  little  after  sunset  and  before  sunrise,  with  the  base 
towards  the  sun.  It  is  most  clear  about  the  beginning  of 
March  in  the  evening,  and  in  September  in  the  morning, 
but  in  the  torrid  zone  it  is  constantly  seen.  It  is  generally 
supposed  to  proceed  from  the  sun's  atmosphere. 

Questions.— 1.  What  is  the  figure  of  the  sun?  2.  Describe  the 
motions  of  the  sun.  3.  How  i.s  it  made  evident  that  the  sun  has  a 
rotation  round  his  axis.''  4.  What  is  said  of  the  spots  that  have  been 
seen  in  the  sun  .''  5.  What  does  Dr.  Herschel  consider  the  sun  to  be  ? 
— The  spots  ?  6.  Describe  the  zodiacal  light.  7.  In  what  proportion 
do  the  planets  receive  light  and  heat  from  the  sun  ?  {see  Appendix.) 
8.  What  rule  is  given  ?  9.  What  is  said  of  the  attraction  of  bodies  ? 
10.  What  is  the  rule  for  finding  the  distances  of  the  planets  from  the 
sun?  II.  What  was  ascertained  by  Kepler?  12.  What  is  the  rule 
for  finding  how  many  times  one  planet  is  greater  than  another? 
[Note.  When  any  body,  revolving  round  the  sun, is  nearest  to  him,  it  is 
said  to  be  in  its  perihe'lion  ;  and  when  it  is  most  distant,  in  its  aphe'- 
lion  (pron.  af-e'le-un.)  The  common  centre  aboui  vh'ch  the  sun  re- 
volves in  its  periodical  motion  is  always  found  to  be  exceedingly  near 
the  sun,  and  most  commonly  within  it :  it  may,  therefore,  without  any 
material  error,  be  regarded  as  the  centre  of  the  planetary  system.} 


LESSON  43. 

Mercury  and  Venus. 

Elonga'tion,  a  planet's  elongation,  or  its  angular  distance  from  the 
sun,  IS  an  angle  formed  at  the  earth  by  two  lines,  one  drawn 
from  the  earth  to  the  sun,  and  one  from  the  earth  to  the  planet. 

Disk,  the  face  of  the  sun  and 'moon,  as  it  appears  to  us  on  the 
earth. 

Mercury  is  seldom  visible  to  the  inhabitants  of  the  earth, 
for  its  greatest  apparent  distance  from  the  sun,  or  its  great- 
est elongation,  is  not  more  than  twenty-eight  degrees,  and 
its  reflected  light  is  absorbed  in  the  more  powerful  rays  of 
the  sun.  He  always  appears  on  the  same  side  of  the  heavens 
with  the  sun  ;  of  course,  he  can  be  seen  in  the  east,  only  in 
the  morning  a  little  before  sunrise,  and  in  the  west  in  the 
evening  a  little  after  sunset.  When  viewed  with  a  telescope 
of  high  magnifying  power,  he  exhibits  nearly  the  same  pha- 
ses as  the  moon,  and  they  are  to  be  accounted  for  in  the 
same  manner.     Mercury  revolves  round  the  sun  at  nearly 


96 


VENUS. 


llie  mean  distance  of  thirty  seven  millions  of  miles,  and  com-  ■ 
pletes  his  revolution  in  about  three  months.  According  to  Sir  ^ 
Isaac  Newton,  the  heat  and  light  of  the  sun  on  the  surface  \ 
of  Mercury,  are  almost  seven  times  as  intense  as  on  the  sur-  ; 
face  of  the  earth  in  the  middle  of  summer ;  which,  as  he  ; 
found  by  experiments  made  for  that  purpose  with  a  ther-  i 
mometer,  is  sufficient  to  make  water  fly  off  in  steam  and  va-  i 
poui.  Such  a  degree"  of  heat,  therefore,  must  render  Mer- 
cury uninhabitable  to  creatures  of  our  constitution  ;  and  if  ■ 
bodies  on  its  surface  be  not  inflamed  and  set  on  fire,  it  must  ^ 
be  because  their  degree  of  density  is  proportionably  greater  j 
than  that  of  such  bodies  is  with  us.  When  Mercury  passes  ^ 
over  the  sun's  face,  or  is  between  us  and  the  sun,  this  is  : 
called  his  transit,  and  the  planet  appears  like  a  black  spot  in  1 
the  sun's  disk.  The  light  emitted  by  Mercury  is  a  very  \ 
bright  white.  I 

Fair  Venus  next  fulfils  her  larger  round,  : 

With  softer  beams,  and  milder  glory  crowned  ; 
Friend  to  mankind,  she  glitters  from  afar,  ; 

Now  the  bright  evening,  now  the  morning  star. 

Baker. 

Venus    is  computed  to  be  sixty-eight  millions   of  miles    i 
from  the  sun,  and  completes  her  annual  rotation  in  about    ] 
seven  and  a  half  months,  turning  on  her  axis  in  a  little  less  ;! 
than  twenty  four  hours.     The  light,  which  this  planet  re-  ] 
fleets,  is  very  brilliant,  and  often  renders  her  visible  to  the    ; 
naked  eye  in  the  day-time.     When  Venus  is  to  the  west  of  ■] 
the  sun,  she  rises  before  the  sun,  and  is  called  the  morning  ^ 
star  ;  when  she  appears  to  the  east  oi*  the  sun,  siie  shines  in   ^ 
the  evening,  and  is  then  called  the  evening  star.     She  is  in  i 
each  situation  alternately,  for  about  two  hundred  and  ninety   ] 
days ;  and,  during  the  whole  of  her  revolution,  she  appears, 
through  a  telescope,  to  have  all  the  various  shapes  and  ap- 
pearances of  the  moon.     As  the  orbit  of  Venus  is  within   , 
that  of  the  earth,  like  Mercury,  she  sometimes  passes  over  the 
sun's  face,  and  her  transits  have  been  applied  to  one  of  the 
most  important  problems  in  astronomy, — that  of  determining 
the  true  distances  of  the  planets  from  the  sun.     The  atmo- 
sphere of  Venus  has  been  calculated  to  be  fifty  miles  high  ; 
this  has  been  learned  from  observing  her  transits,  when  her 
Etmosphere  was  seen  to  throw  a  shade  on  the  sun's  disk  h 


THE  EARTH.  97 

about  five  seconds  before  the  more  opaque  part  touched  his 
edge.  When  the  elongation  of  Venus  is  about  forty  de- 
grees, her  lustre  far  exceeds  that  of  the  moon,  at  the  same 
apparent  distance  from  the  sun.  For  though  the  moon  re- 
flects more  light  to  us  than  Venus  does,  yet  this  light  is  dull, 
and  has  none  of  the  briskness  which  attends  the  beams  of 
Venus,  This  difference  is  supposed  to  arise  from  the  cir- 
cumstance of  Venus  having  an  atmosphere  far  more  dense 
than  that  of  the  moon. 

Questions. — 1.  What  is  the  appearance  of  Mercury  ?  2.  What  is 
the  length  of  his  year  ? — Distance  from  the  sun  ?  3.  Why  is  it  seldom 
seen  ?  4.  What  is  its  greatest  elongation  ?  5.  What  calculation 
did  Newton  make  with  respect  to  the  light  and  heat  of  Mercury  ?  6. 
What  must  be  the  consequence  of  such  a  degree  of  heat  ?  7.  What  is 
called  a  transit  of  Mercury  ?  8.  What  is  the  distance  of  Venus  from 
the  sun  ? — Lene;th  of  her  year  ? — Day  ?  9.  When  is"  Venus  evening 
and  when  morning  star  ? — How  long  in  each  situation  ?  10.  To  what 
purpose  have  her  transits  been  applied  .''  11.  What  is  said  of  her  at- 
mosphere ?  12.  When  is  the  lustre  of  Venus  greatest,  and  to  what  is 
it  attributed .'' 


LESSON  44. 

The  Earth. 

Merid'ian,  a  great  ci;rcle  passing  through  the  poles  of  the  world, 
<ind  also  through  both  zonith  and  nadir  ;  it  crosses  the  equator 
at  right  angles,'and  divides  the  sphere  into  two  hemispheres, 
the  eastern  and  the  western  ;  it  has  its  poles  at  the  east  and  west 
points  of  the  horizon. 

The  planet  which  we  inhabit  is  called  the  earth.  It  re- 
.^olves  about  the  sun  at  the  mean  distance  of  ninety-five,  or, 
as  some  state,  of  ninety-three  millions  of  miles,  It  com- 
pletes this  revolution  in  a  year,  and  turns  on  its  axis  in  a  day, 
or  twenty-four  hours.  If  the  earth  were  seen  from  the  sun, 
it  would  appear  to  describe,  while  revolving  in  its  orbit,  a 
circle  among  the  stars.  But  to  us  on  the  earth,  the  sun  ap- 
pears to  describe  precisely  the  same  circle,  only  beginning 
at  the  opposite  point.  That  imaginary  great  circle  in  the 
heavens,  which  the  sun  appears  to  describe  in  the  course  of 
the  year,  is  called"  the  ediptic.  The  apparent  diurnal,  or 
dailj/  motion  of  th-  sun  is  very  different  from  the  path  which 
it  appears  to  traverse  in  the  course  of  a  year.  The  former 
9 


^  CELESTIAL   LATITUDE    AND    LONGITUDE. 

) 

is  obi3erved  by  the  most  inattentive  spectator ;  but  the  ^ 
knowledge  of  the  latter  must  be  the  resuh  of  patient  ob-  . 
servation.  i 

The  other  primary  planets,  when  seen  from  the  sun,  do 
not  describe  exactly  the  same  circle  among  the  stars,  that  1 
the  earth  docs  ;  but  are  sometimes  on  one  side  of  the  ecliptic  \ 
and  sometimes  on  the  other.  But  none  of  them,  except  i 
Juno,  Pallas,  and  Ceres,  are  ever  farther  distant  from  the  ] 
ecliptic  than  eight  degrees.  So  that  within  a  zone  or  belt  \ 
of  sixteen  degrees,  that  is,  eight  degrees  on  each  side  of  the  i 
ecliptic,  the  planets,  except  those  just  named,  are  always  to  I 
be  found.  This  zone,  or  broad  belt,  is  called  the  Zodiac,  s 
The  ecliptic  then  is  an  imaginary  circle  in  the  heavens  pass-  i 
ing  through  the  middle  of  the  zodiac,  and  situated  in  the  1 
plane  of  the  earth's  orbit.  A  plane  is  an  even  level  surface,  j 
If  you  suppose  a  smooth  thin  solid  plane  cutting  the  sun  J 
through  the  centre,  extending  out  as  far  as  the  fixed  stars,  | 
and  terminating  in  a  circle  which  passes  through  the  middle  * 
of  the  zodiac  ;  in  this  plane  the  earth  would  move  in  its  re-  ^ 
volution  round  the  sun  ;  it  is  therefore  called  the  plane  of  5 
the  earth's  orbit.  The  points,  where  the  orbit  of  any  hea- 
venly body  cuts  the  plane  of  the  ecliptic,  are  called  the  nodes  ] 
of  that  body.  The  point,  where  the  body  passes  from  the  ' 
north  side  of  the  plane  of  the  ecliptic  to  the  south,  is  called  ] 
its  descending  node ;  where  it  passes  from  the  south  to  the  \ 
north,  its  ascending  node.  J 

The  ecliptic,  as  well  as  every  other  circle,  great  or  small,  5 
is  divided  into  three  hundred  and  sixty  degrees  ;  but  it  has  j 
also  another  division  into  twelve  signs,  of  thirty  degrees  each,  \ 
called  the  twelve  signs  of  the  zodiac.  These  signs  derive 
their  names  from  clusters  of  stars,  or  constellations,  which,  as  \ 
the  ancients  imagined,  resembled  certain  animals.  They  are  f, 
most  commonly  represented  by  characters,  and  the  names  -, 
given  them  should  be  made  familiar ;  for  the  sun,  as  he  ap-  j 
pears  to  move  round  in  the  ecliptic,  seems  to  enter  these  clus-  J 
ters  of  stars,  and  is  therefore  said  to  be  in  this  or  that  sign,    j 

If  the  axis  of  the  earth  be  supposed  to  extend  both  ways  J 
to  the  starry  heavens,  its  places  or  points  among  the  stars  | 
are  the  celestial  poles,  one  north  and  the  other  south,  direct-  | 
ly  over  or  beyond  the  poles  of  the  earth  of  the  same  name.  ^ 
If  the  plane  of  the  earth's  equator  were  extended  every  way  | 
to  the  starry  heavens,  the  circle  it  would  make  among  the  J 


CELESTIAL   LATITUDE    AND   LONGITUDE.  99 

Stars  is  called  the  celestial  equator.  Now  the  celestial  equa- 
tor does  not  coincide  with  the  ecliptic,  but  makes  an  angle 
with  it  of  twenty-three  degrees  and  twenty-eight  minutes, 
that  is,  the  axis  of  the  earth  is  not  perpendicular  to  the  plane 
of  the  ecliptic,  but  is  inclined  twf^nty-three  degrees  and 
twenty-eight  minutes.  Thus  we  have  two  great  circles,  the 
ecliptic  and  equator,  passing  through  the  heavens  eastwardly 
and  westwardly,  from  either  of  which  the  latitude  of  the  hea- 
venly bodies  might  be  estimated.  But  astronomers  have  se- 
lected the  ecliptic  for  this  purpose,  and  have  supposed  lines 
or  circles  to  cross  it  at  right  angles,  as  the  meridians  do  the 
equator  ;  which  lines  or  circles  are  called  secondaries  to  the 
ecliptic.  The  points  where  all  the  secondaries  meet,  are 
called  i\\Q poles  of  the  ecliptic ;  which  points  are  twenty-three 
degrees  twenty-eight  minutes  from  the  celestial  poles.  Hence 
the  latitude  of  a  heavenly  body  is  its  distance  from  the 
ecliptic,  measured  on  a  secondary  to  the  ecliptic  ;  and  like 
latitude  on  the  earth,  it  can  never  exceed  ninety  degrees. 
The  longitude  of  a  heavenly  body  is  the  distance  of  a  se- 
condary to  the  ecliptic,  reckoned  from  some  given  uniform 
secondary,  called  the  prime  secondary.  But  the  longitude 
of  heavenly  bodies,  unlike  longitude  on  the  earth,  is  reckon- 
ed only  easticard;  it  may  extend,  therefore,  to  three  hun- 
dred ajid  sixty  degrees.  It  is  usually  stated  in  signs,  degrees, 
minutes,  and  so  forth  ;  and  the  prime  secondary,  from  which 
it  is  reckoned,  cuts  the  ecliptic  in  the  beginning  of  the  sign 
Aries,  a  point  where  the  celestial  equator  crosses  the  ecliptic. 
If  a  secondary,  for  instance,  passing  through  a  heavenly 
body,  cuts  the  ecliptic  eighteen  degrees  in  the  sign  Capri- 
corn, then,  since  the  first  point  of  Capricorn  is  nine  signs 
eastward  from  the  first  point  of  Aries,  the  longitude  of  that 
body  is  nine  signs,  eighteen  degrees.  But  it  is  often  impor- 
tant to  know  the  distance  of  a  heavenly  body  from  the  celes- 
tial equator,  as  well  as  from  the  ecliptic.  This  distance  is 
its  declination,  and  is  reckoned  on  a  meridian,  as  latitude  is 
on  the  earth.  Its  distance  from  the  beginning  of  Aries, 
reckoned  on  the  equator,  is  its  right  ascension ;  which,  like 
celestial  longitude,  is  reckoned  through  the  whole  circle,  or 
three  hundred  and  sixty  degrees.  Two  planets  are  said  to 
be  in  conjunction  with  each  other,  when  they  have  the  same 
longitude,  or  are  in  the  same  degree  of  the  ecliptic  on  the 
same  side  of  the  heavens,  though  their  latitude  be  different. 


100  DAY   AND    NIGHT. 

They  are  said  to  be  in  opposition,  when  their  longitudes 
differ  half  a  circle,  or  they  are  in  opposite  sides  of  the 
heavens. 

Questions.— 1.  What  is  the  ecliptic  ?— explain.  2.  What  is  the 
zodiac  ? — explain.  ^  What  ia  meani  t>y  tlie  plane  of  the  earth's  orbit  ? 
4.  What  are  nodes  .''  5.  What  are  the  divisions  of  the  ecliptic  .''  6. 
What  are  the  celestial  poles.''  7.  What  is  the  celestial  equator .-'  8. 
How  is  the  axis  of  the  earth  situated  with  regard  to  the  plane  of  the 
ecliptic.^  9.  What  are  the  poles  of  the  ecliptic  .•*  10.  What  is  the  la- 
titude of  a  heavenly  body  .^  11.  The  longitude.''  12.  How  is  the 
longitude  of  a  heavenly  body  reckoned  and  stated  ?  13.  What  exam- 
ple is  given  .'  14.  What  is  the  declination  of  a  heavenly  body.  15. 
Right  ascension  .''  16.  When  are  two  planets  said  to  be  in  conjunct 
tion  ?  17.  In  opposition  ?  [Note.  The  points  at  which  the  ecliptic 
cuts  the  celestial  equator  are  called  the  equinoctial  points.  Those  two 
points  of  the  ecliptic  farthest  from  the  equator  are  called  sol'stices. 
Ap'ogec,  that  point  of  the  orbit  of  the  moon  which  is  farthest  from  the 
earth.  Per'igee,  that  point  which  is  nearest  to  the  earth.]  18.  Look 
at  fig.  40.  and  point  out  the  ecliptic,  zodiac,  and  signs  of  the  zodiac. 


LESSON  45. 

Day  and  Night. 

Ver'nal,  belonging  to  the  spring. 

Intersect',  to  cut,  to  divide  each  other  mutually. 

By  the  diurnal  motion  of  the  earth,  the  same  phenomena 
appear  as  if  all  the  celestial  bodies  turned  round  it ;  so  that 
in  its  rotation  from  west  to  east,  when  the  sun  or  a  star  just 
appears  on  the  eastern  side  of  the  horizon,  it  is  said  to  be 
rising,  and  as  the  earth  continues  its  revolution,  it  seems 
gradually  to  ascend  till  it  has  reached  its  meridian  ;  here  the 
object  has  its  greatest  elevation,  and  begins  to  decline  till  it 
set,  or  become  invisible  on  the  western  side.  In  the  same 
manner  the  sun  appears  to  rise  and  run  his  course  to  the 
western  horizon,  where  he  disappears  and  night  ensues,  till 
he  again  illuminate  the  same  part  of  the  earth  in  another 
diurnal  revolution.  One  half  of  the  earth's  surface  is  con- 
stantly illuminated,  and  by  the  regular  motion  of  the  earth 
on  its  axis,  every  place  is  successively  brought  into  light  and 
immersed  in  darkness.  If  the  axis  of  the  earth  were  always 
perpendicular  to  the  plane  of  the  ecliptic,  the  days  would 
every  where  be  of  the  same  length,  and  just  as  long  as  the 


DAY    AND    NIGHT. 


101 


nights.     For  an  inhabitant  at  the  equator,  and  one  on  the 
same  meridian  towards  the  poles,  would  come  into  the  light 
at  the  same  time,  and,  on  the  other  side,  would  immerge  into 
darkness  at  the  same  time.     And  since  the  motion  of  the 
earth  is  uniform,  they  would  remain  in  the  dark  hemisphere 
just  as  long  as  in  the  light ;  that  is,  their  day  and  night  would 
be  equal; — the  plane  of  the  ecliptic  would  coincide  with  the 
plane  of  the  equator.     But  as  the  ecliptic  and  equator  make 
an  angle  with  each  other  of  twenty-three  degrees  and  twenty- 
eight  nnnutes,  or  in  other  words,  as  the  axis  of  the  earth  has 
such  an   inclination  to  the  plane  of  its  orbit,  it  is  manifest 
that,  except  the  earth  be  in  that  part  of  its  orbit  where  the 
ecliptic  cuts   the   equator,  an  inhabitant  at  the  equator  and 
one  on  the  same  meridian  towards  the  poles,  will  not  come 
into  the  light  at  the  same  time,  nor,  on  the  other  side,  im- 
merge into  darkness  at  the  same  time.     And  since  the  axis 
of  the   earth   always  preserves  the   same  inclination,  they 
will, — except  at  the  points  w^here  the  two  great  circles  inter- 
sect each  other, — remain  in  the  dark  and  light  hemispheres 
different  times  ,  that  is,  their  day  and  night  will  be  unequal. 
The  points  where  the  equator  cuts  the  ecliptic  are  at  the  be- 
ginning of  the  signs  Libra   and   Aries.     The   earth  is   at 
these  points  of  its  orbit,  or,  as  it  is  commonly  said,  the  sun 
enters  the   sign  Aries  on  the   twentieth   of  March,  and  the 
sign  Libra  on  the  twenty-third  of  September.     Hence   at 
these  periods,  and  at  no  others,  the  days  and  nights  are  equal 
all   over  the  world ;  and  on  this   account  they   are  called 
equinoxes  ;  the  first  the  vernal,  and  the  second  the  autum- 
nal equinox.     At  these  seasons,  the  sun  rises  exactly  in  the 
east  at  six  o'clock,  and  sets  exactly  in  the  west  at  six  o'clock ; 
— the  light  of  the  sun  is  then  terminated  by  the  north  and 
south  poles,  and  as  all  parts  of  the  earth  turn  round  once  in 
twenty-four  hours,  every  place  must  receive  the  rays  twelve 
hours,   and  be  deprived  of  them  for  tho  same  time.     But  at 
other  seasons,  when  the  rays  of  light  are  not  terminated  by 
the  north  and  south  poles,  but  extend  over  the  one  and  do 
not  reach  the  other,  it  must  be  manifest,  from  a  moment's 
inspection  of  the  circles  drawn  on  globes,  or  common  maps 
of  the  world,  that  day  and  night  will  be  unequal  in  all  places 
except  those  situated  on  the"  equator,  where  they  will  be 
always  equal.     At  the  poles  there  is  but  one  day  and  one 
night  in  a  year,  each  of  six  months.     The  sun  can  never 
9* 


102  CHANGES  OF  THE  SEASOI^S^. 

shine  beyond  a  pole  farther  than  twenty-three  degrees  and 
twenty-eight  minutes ;  for  that  is  the  extent  of  his  declina- 
tion ;  and  when  he  has  declination  from  the  celestial  equa- 
tor either  north  or  south,  he  must  shine  beyond  one  pole  and 
not  to  the  other ;  the  days^^  therefore,  will  be  longest  in  one 
hemisphere  when  they  are  shortest  in  the  other. 

The  subject  of  this  lesson  may  be  illustrated,  by  hanging 
any  round  body  above  or  below  the  level  of  a  candle  so  as  to 
correspond  with  the  sun's  declination.  It  will  be  seen, 
that  the  light  shines  over  one  pole  and  does  not  reach  the 
other.  If  the  ball  be  then  turned  round,  it  will  be  observed, 
that  the  circles  performed  by  any  parts  of  the  surface  are 
unequally  divided  by  the  light ;  that  it  will  be  constant  day 
or  night  near  the  north  pole,  as  the  ball  is  depressed  or  ele- 
vated, and  that  all  the  phenomena  will  be  reversed  in  the 
other,  or  lower  hemisphere. 

Questions. — 1.  What  phennomena  appear  from  the  diurnal  motion 
of  the  earth  ?  2.  Under  what  circumstances  would  the  days  and  nights 
bo  every  whore  of  tlie  same  length  ? — Why  ?  3.  Why  is  not  the  day 
and  night  aKvnys  equal  to  an  inhabitant  at  the  "equator,  and  to  one  on 
the  same  meridian  towards  the  poles  ?  4.  At  what  points  does  the 
equator  cut  the  ecliptic  ?  5.  When  is  the  earth  at  those  points  of  its 
orbit  ? — and  what  happens  at  these  periods  ?  G.  At  other  seasons  ?  7. 
What  is  said  of  day  and  night  at  the  poles?  8.  How  may  the  subject 
of  this  lesson  be  illustrated  ?  9.  Look  at  fig.  40,  and  illustrate  th» 
rauations  in  the  lengths  of  the  days  and  nights. 


LESSON  46. 

Changes  of  the  Seasons, 

Obliq'uity  of  the  Ecliptic,  the  angle  which  the  ecliptic  makes 
with  the  equator. 

Look  nature  through,  'tis  revolution  all  ; 

All  change,  no  death.     J)ay  follows  night,  and  night 

The  dying  day.     Stars  rise  and  set,  and  rise. 

Earth  takes  th*  example ;  see,  the  summer  gay, 

With  her  green  chaplet  and  ambrosial  flowers, 

Droops  into  pallid  Autumn.     Winter  gay, 

Horrid  with  frost,  and  turbulent  with  storm, 

Blows  Autumn  and  his  golden  fruits  away  ; 

Then  melts  into  the  Spring.     Soft  Spring,  with  breatli 

Favonian^  from  warm  chambers  of  the  south, 


CHANGES^  OF   THE  SEASONS.  ICfil 

Recals  the  first.     All,  to  reflourish,  fades  ; 

As  in  a  wheel,  all  sinks,  to  reascend  : 

Emblem  of  man,  who  passes,  not  expires. — Thomson. 

The  orbit  in  which  the  earth  revolves  in  his  annual 
course  round  the  sun  is  not  a  circle  but  an  ellipse  or  oval  ; 
and  we  are  more  than  three  millions  of  miles  nearer  to  the 
sun  in  December  about  the  time  of  the  winter  solstice,  than 
we  are  in  June  about  the  time  of  the  summer  solstice.  Now 
as  heat  and  l>ght  from  the  sun  are  greater  as  the  distance  is 
less,  it  is  manifest  that  this  circumstance  would  occasion  a 
variation  in  the  temperature  of  the  air,  like  that  of  our  sea- 
sons, if  the  equator  always  coincided  with  the  ecliptic.  But 
the  seasons  with  us,  in  north  latitude,  are  not  in  the  least  de- 
gree occasioned  by  this  circumstance,  but  by  the  direction 
in  which  the  sun's  rays  fall  upon  us.  When  they  fall  per- 
pendicularly, or  most  nearly  so,  the  season  is  warmest ;  and 
when  they  fall  most  obliquely,  or  in  a  slanting  manner,  the 
season  is  coldest.  The  cause  of  the  difference  in  the  obli- 
quity of  the  sun's  rays  is  the  obliquity  of  the  ecliptic.  The 
effect  of  obliquity,  in  regard  to  rays  will  be  evident,  if  ai 
board  be  held  perpendicularly  before  a  fire.  It  will  then  re- 
ceive a  body  of  rays  equal  to  its  breadth.  But  if  it  be  placed 
obliquely,  at  an  angle  of  forty-five  degrees,  then  only  half 
the  rays  will  fall  on  its  surface,  arid  the  other  half  will  pass 
over  it ;  so  it  is  with  the  surface  of  the  earth  in  summer  and 
winter.  The  circumstance  also,  that  the  days  are  longest, 
whether  in  north  or  south  latitude,  when  the  sun's  rays  fall 
in  the  greatest  quantity  and  most  directly  at  any  place,  con- 
tributes much  to  the  warmth  of  summer  and  the  cold  of  win- 
ter. In  northern  countries,  where  the  days  are  eighteen  or 
twenty  hours  long,  or  where  the  sun  is  above  the  horizon  for 
any  number  of  days  together,  the  heat  of  summer  is  equal  to 
that  of  any  part  of  the  world. 

Since  the  degree  of  heat  from  the  sun  increases  as  the 
earth's  distance  diminishes,  and  this  distance  is  least  when 
it  is  summer  in  south  latitude,  and  greatest  v/hen  it  is  sum- 
mer in  north  latitude,  a  greater  degree  of  heat,  therefore, 
must  be  received  in  summer  in  south  latitude,  than  in  sum- 
mer in  north  latitude.  But  to  compensate  for  a  less  degree 
of  heat,  the  inhabitants  in  north  latitude  have  longer  sum- 
mers than  those  in  south  latitude.     For  as  the  sun  is  not  in 


104  THE  MOON. 

the  centre  of  an  ellipse  but  in  the  focus,  the  earth  must 
move  farther  in  its  orbit  in  one  pari  of  its  revolution  than  in 
the  other.  It  moves  slovver  also  as  it  is  farther  from  the 
sun  ;  and  our  summers  are  found  to  be  eight  days  longer 
than  the  summers  in  south  latitude ;  that  is,  between  the 
vernal  and  autumnal  equinoxes  there  are  eight  days  more, 
than  between  the  autumnal  and  vernal. 

It  is  well  known  that  the  degree  of  heat  is  not  greatest, 
when  the  days  are  longest.  We  have  the  warmest  weather 
in  the  latter  part  of  July,  and  in  the  first  of  August ;  and 
our  coldest  month  is  January.  To  account  for  this  it  has 
been  stated,  that  a  body  once  heated  does  not  grow  cold 
again  instantaneously,  but  gradually ;  now  as  long  as  more 
heat  comes  from  the  sun  in  the  day,  than  is  lost  in  the  night, 
the  heat  of  the  earth  and  air  will  be  daily  increasing,  and 
this  must  evidently  be  the  case  for  some  weeks  after  the 
longest  day,  both  on  account  of  the  number  of  rays  which 
fall  on  a  given  space,  and  also  from  the  perpendicular  di- 
rection of  those  rays.  It  is  for  the  same  reason,  that  the 
warmest  part  of  the  day  is  not,  when  the  sun  is  at  the  me- 
ridian, but  ai)out  two  or  three  o'clock  in  the  afternoon. 

Questions. —  I.  When  are  those  who  live  in  north  latitude  nearest 
the  sun  ?  2.  What  would  be  the  conscquenfo  ifflic  equator  coincided 
with  the  eclipric  ?  3.  What  occasions  the  seasons  witli  us  ?  4.^  How 
may  the  effect  of  obliquity  in  regard  to  the  sun's  rays  be  made  evident  ? 
5.  Wliat  contributes  much  to  the  warmth  of  summer?  6.  What  is 
said  of  north  and  south  latitudes  as  respects  the  degree  of  heat  ? — Ex- 

fdain.     7.  Why  is  not  the  degree  of  heat  greatest  when  the  days  are 
ongest  ?   8.  Look  at  fig.  40,  and  illustrate  the  diversity  of  the  seasonB. 


LESSON  47. 
The  3Ioon. 

Quad'rature,  the  first  and  last  quarter  of  the  moon. 
Lu'nar,  relating  to  the  moon.     Luna'tion,  the  revolution  of  the 
moon. 

The  moon  is  a  secondary  planet,  revolving  round  the 
earth  in  about  twenty-nine  days  and  a  half,  and  is  carried 
with  the  earth  round  the  sun  once  a  year.  Its  distance 
from  the  earth  is  about  two  hundred  and  forty  thousand 
miles ;  and  it  turns  on  its  axis  in  the  same  time  that  it  per- 


THE  MOON. 


M 


forms  its  revolution  round  the  earth.  The  light  of  the  sun 
illuminates  one  half  of  its  surface,  and  leaves  the  other  in 
darkness.  Of  this  illumination  we  perceive  different  de- 
grees, according  to  the  various  positions  of  the  moon,  with 
respect  to  the  sun  and  the  earth.  We  see  one  half  of  its 
body  enlightened,  or  a  fall  moon,  wheh  it  is  placed  in  oppo- 
sition to  the  sun,  or  when  the  sun  is  in  one  part  of  the  hea- 
vens, as  west,  and  the  moon  in  the  opposite  part,  as  east. 
When  the  moon  is  in  conjunction  with  the  sun,  or  in  that 
part  of  its  orbit  which  is  between  the  earth  and  the  sun,  its 
enlightened  surface  is  turned  from  us,  which  renders  it  in- 
visible ;  this  is  the  time  of  the  new  moon.  When  the  moon 
appears  in  the  intermediate  part  of  its  orbit,  between  the 
conjunction  and  opposition,  it  is  in  its  quadratures,  and  about 
half  of  its  illuminated  surface  is  turned  towards  us. 

As  the  moon  illuminates  the  earth  by  light  reflected  from 
the  sun,  so  she  is  reciprocally  illuminated  by  the  earth  which 
reflects  the  sun's  rays  to  the  surface  of  the  moon.  As  the 
surface  of  the  earth  is  more  than  thirteen  times  greater  than 
that  of  the  moon,  the  earth  must  appear  to  the  inhabitants 
of  the  moon  thirteen  times  larger  than  the  moon  does  to  us, 
and  it  will  exhibit  the  same  pliases,  but  in  an  opposite  order. 
As  the  rotation  of  the  moon  on  her  axis  is  performed  in  the 
same  time  that  she  goes  once  round  the  earth, — which  is 
evident  from  her  always  presenting  the  same  face  to  us  dur- 
ing the  whole  of  her  monthly  revolution, — it  is  plain,  that 
the  inhabitants  of  one  half  of  the  lunar  world  are  totally  de- 
prived of  a  sight  of  the  earth,  unless  they  travel  to  the  oppo- 
site hemisphere. 

The  face  of  the  moon  appears  to  have  shades  of  different 
colours.  If  viewed  through  an  ordinary  telescope,  her  sur- 
face will  appear  diversified  with  long  tracts  of  mountains 
and  cavities.  It  has  been  ascertained  that  these  are  moun- 
tains from  the  shadows  which  they  cast,  and  some  of  them 
are  supposed  to  be  volcanic. 

The  difference  between  the  rising  of  the  moon  on  one  day 
and  the  preceding  is  generally  about  fifty  minutes.  But  in 
places  of  considerable  latitude,  there  is  a  remarkable  differ- 
ence about  the  time  of  harvest,  when  at  the  season  of  full 
moon  she  rises  for  several  nights  together  only  about  twenty 
minutes  later  on  the  one  day  than  on  that  immediately  pre- 
ceding.    By  thus  succeeding  the  sun  before  ihe  twilight  i& 


106  THE    HARVEST    M«ON. 

ended,  the  moon  prolongs  the  light,  to  the  great  benefit  of 
those  who  are  engaged  in  gathering  in  the  fruits  of  the 
earth ;  and  hence  the  full  moon  at  this  season  is  called  the 
harvest  moon.  It  is  believed  that  this  was  observed  by  per- 
sons engaged  in  agriculture,  at  a  much  earlier  period  than 
it  was  noticed  by  astronomers.  The  phenomenon  may  be 
easily  explained  by  the  assistance  of  a  globe  :  and  it  is  oc- 
casioned by  the  moon's  orbit  lying  sometimes  more  oblique 
to  the  horizon  than  at  others. 

The  Harvest  Moon. 
All  hail !  thou  lovely  queen  of  night, 
Bright  empress  of  the  starry  sky  1 
The  meekness  of  thy  silvery  light 

Beams  gladness  on  the  gazer's  eye, 
While  from  thy  peerless  throne  on  high 

Thou  shinest  bright  as  cloudless  noon, 
And  bidd'st  the  shades  of  darkness  fly 

Before  thy  glory — Harvest  moon  ! 
In  the  deep  stillness  of  the  night, 
When  weary  labour  is  at  rest. 
How  lovely  is  the  scene  ! — how  bright 

The  wood — the  lawn — the  mountain's  breast, 
When  thou  fair  moon  of  Harvest !  hast 

Thy  radiant  glory  all  unfurled. 
And  sweetly  smilest  in  the  west, 

Far  down  upon  the  silent  world. 
Shine  on,  fair  orb  of  light !  and  smile 

Till  autumn  months  have  passed  away, 
And  labour  hath  forgot  the  toil 

He  bore  in  summer's  sultry  ray  ; 
And  when  the  reapers  end  the  day. 

Tired  with  the  burning  heat  of  noon, 
They  '11  come  with  spirits  light  and  gay. 
And  bless  thee — lovely  Harvest  Moon  ! 

W.  Millar. 
Questions. — 1.  In  what  time  does  the  moon  revolve  round  the 
earth  ?  2.  At  what  distance  is  it  from  the  earth  ?  3.  In  what  time 
does  it  turn  on  its  axis?  4.  What  is  said  of  the  illumination  of  the 
moon  ?  5.  How  does  the  earth  appear  as  seen  from  the  moon  ?  6. 
How  does  the  face  of  the  moon  appear  when,  viewed  through  a 
telescope  ?  7,  What  is  the  Harvest  Moon  ?  8.  By  what  is  it  occa« 
sioned  ? — 9.  Look  at  fig.  41,  and  illustrate  the  phases  of  the  moon. 


THE  TIDES.  107 


LESSON  48. 


i 


The  Tides. 


'The  sea  is  observed  to  flow  for  certain  hours  from  the 
south  towards  the  north.  In  this  motion,  which  lasts  about 
six  hours,  the  sea  gradually  swells  ;  so  that  entering  the 
mouths  of  rivers,  it  drives  back  the  waters  towards  their 
heads.  After  a  continual  flow  of  six  hours,  the  sea  seems 
to  rest  for  about  a  quarter  of  an  hour  ;  it  then  begins  to  ebb, 
or  retire  back  again  from  ^orth  to  south  for  six  hours  more ; 
and  the  rivers  resume  their  natural  course.  Then^  after  a 
seeming  pause  of  a  quarter  of  an  hour,  the  sea  again  begins 
to  flow,  as  before,  and  thus  alternately.  This  regular  and 
alternate  motion  of  the  sea  constitutes  the  tides.  They  are 
chiefly  occasioned  by  the  attraction  of  the  moon,  but  are  af- 
fected by  that  of  the  sun.  There  are  two  tides  in  about 
twenty-five  hours  ;  and  the  time  of  high  or  low  water  is  eve- 
ry day  fifty  minutes  later  than  on  the  preceding  day.  The 
moon  is  supposed  to  draw  the  earth  towards  itself,  and  to 
act  upon  the  solid  parts  of  it,  in  the  same  manner  as  if  its 
whole  weight  were  in  a  single  point  in  or  near  the  centre. 
Now  the  waters  al  any  place  over  which  the  moon  is  passing, 
will  be  more  attracted  than  the  earth  ;  and  therefore  will  be 
heaped  up  under  the  moon.  But  the  waters  on  the  opposite 
side  of  the  globe  will  be  less  attracted  than  the  earth  ;  con- 
sequently the  earth  is  drawn  away  from  them  ;  and  they  are 
heaped  up,  or,  in  other  words,  it  is  high  water  there.  When 
the  waters  are  elevated  at  the  side  of  the  earth  under  the 
moon,  and  at  the  opposite  side  also,  it  is  evident  they  must 
recede  from  the  intermediate  points,  and  thus  the  attraction 
pf  the  moon  will  produce  high  water  at  two  places  and  low 
water  at  two  places  on  the  earth  at  the  same  time.  The 
tide  is  fifty  minutes  later  every  day,  because  it  is  twenty-four 
hours  and  fifty  minutes  before  the  same  meridian  on  our 
globe  returns  beneath  the  moon.  The  earth  revolves  on  its 
axis  in  about  twenty-four  hours  ;  if  the  moon,  therefore, 
were  stationary,  the  same  part  oC  our  globe  would  return 
beneath  it,  every  twenty-four  hours  ;  but  as  during  our  daily 
revolution  the  moon  advances  in  her  orbit,  the  earth  must 
jnake  more  than  a  complete  revolution  in  order  to  bring  the 


108  ECLIPSES. 

same  meridian  opposite  the  moon ;  we  are  fifty  minutes  in 
overtaking  her,  and  the  tides  are  retarded  for  the  same  rea- 
son that  the  moon  rises  later  on  one  day  than  on  the  pre^ 
ceding. 

The  tides,  though  constant,  are  not  equal ;  but  are  great- 
est when  the  moon  is  in  conjunction  with  the  sun  or  in 
opposition  to  it,  or  at  the  time  of  new  and  full  moon ;  and 
least,  when  in  quadrature  to  it.  This  increase  and  diminu- 
tion constitute  the  sjjriiig  and  7ieap  tides.  The  attraction 
of  the  sun  does  not  raise  tides  ;  its  only  effect  is  to  increase 
or  diminish  those  of  the  moon.  The  tides  are  highest  when 
both  the  luminaries  are  in  the  equator,  and  the  moon  at  the 
least  distance  from  the  earth.  This  happens  at  the  time  of 
the  equinoxes.  The  tide  is  at  the  greatest  height,  not  when 
the  moon  is  in  the  meridian,  but  some  time  afterwards,  be- 
cause the  force  by  which  the  moon  raises  the  tide  continues 
to  act  after  it  has  passed  the  meridian.  The  regular  tides 
are  greatly  affected  by  strong  winds.  Continents  also  stop 
them  in  their  course  from  east  to  west,  and  in  narrow  rivers 
they  are  frequently  very  high  and  sudden,  from  the  resistance 
of  the  banks.  The  advantages  arising  from  tides  are  great. 
By  agitating  the  waters  of  the  ocean  they  preserve  them  in 
a  state  of  purity.  Aided  by  their  means,  ships  of  the  largest 
burden  sail  up  rivers  against  their  natural*  course,  and  con- 
vey into  the  interior  of  countries  tliose  productions  which 
stimulate  the  industry  and  promote  the  happiness  of  nations, 

Questions. — 1.  What  arc  the  tides?  2.  How  are  they  occasion- 
ed .''  3.  How  does  it  appear  that  the  moon  produces  high  water  in  two 
places  at  the  same  time  ?  4.  How  do  you  account  for  the  tide  being 
fifty  minutes  later  every  day?  5.  What  are  spring  and  neap  tides? 
6.  What  is  the  eifect  of  the  sun's  attraction  ?  7.  When  are  tides  highest  ? 
8.  What  produces  irregularity  in  tides  ?  9.  What  advantages  arise 
from  tides  ?     10.  Look  at  figures  42  and  43,  and  explain  the  tides. 


LESSON  49. 

Eclipses. 

An'nular,  having  the  form  of  a  ring,  from  annulus,  a  Latin  "Word 
for  ring. 

The  earth  being  an  opaque  body  enlightened  by  the  sun, 
necessarily  projects  a  shadow  into  the  regions  of  space  in  a 


ECLIPSES    OF    THE    SUN.  109 

contrary  direction.  When  it  so  happens  that  the  moon,  in 
the  course  of  her  revokition  about  the  earth,  falls  into  this 
shadow,  she  loses  the  sun's  light,  and  appears  to  us  eclipsed. 
If  we  suppose  two  straight  lines  drawn  from  the  opposite 
parts  of  the  solar  disk,  touching  the  surface  of  the  earth  on 
opposite  sides  ;  these  lines  will  represent  the  limits  of  the 
shadow,  and  as  the  sun  is  much  larger  than  the  earth,  they 
will  meet  at  a  point  and  cross  each  other  behind  the  earth, 
and  the  shadow  will  thus  take  the  form  of  a  cone.  The 
moon  can  come  within  the  shadow  of  the  earth  only  when 
it  is  full,  or  in  opposition  to  the  sun.  But  the  moon  is  not 
eclipsed  every  time  it  is  full,  because  its  orbit  does  not  coincide 
with  the  plane  of  the  earth's  orbit,  one  half  being  about  five 
degrees  and  a  third  above  it,  and  the  other  half  as  much  below 
it ;  and  unless  the  full  moon,  therefore,  happen  in  or  near 
one  of  the  nodes,  that  is,  in  or  near  the  points  in  which  the 
two  orbits  intersect  each  other,  she  will  pass  above  or  below 
the  shadow  of  the  earth,  in  which  case  there  can  be  no 
eclipse.  If  the  moon  be  within  twelve  degrees  from  the 
node,  at  the  time  when  she  is  full,  there  will  be  a  partial  or 
total  eclipse,  according  as  a  part,  or  the  whole  of  her  disk 
falls  within  the  earth's  shadow.  As  the  shadow  is  consi- 
derably wider  than  the  moon's  diameter,  an  eclipse  of  the 
moon  lasts  sometimes  three  or  four  hours.  It  is  by  knowing 
exactly  at  what  distance  the  moon  is  from  the  earth,  and  of 
course  the  width  of  the  earth's  shadow  at  that  distance,  that 
eclipses  are  calculated  with  the  greatest  accuracy,  for  many 
years  before  they  happen.  Lunar  eclipses  are  visible  over 
every  part  of  the  earth  that  has  the  moon  at  that  time  above 
the  horizon  ;  and  the  eclipse  appears  of  the  same  magnitude 
to  all  from  the  beginning  to  the  end.  That  faint  reddish 
colour,  which  the  moon  exhibits  in  the  midst  of  an  eclipse, 
is  supposed  to  proceed  from  the  rays  of  light,  which  are  re- 
fracted by  the  earth's  atmosphere,  and  fall  upon  the  surface 
of  the  moon. 

An  eclipse  of  the  sun  is  caused  by  an  interposition  of  the 
moon  between  the  sun  and  the  earth.  This  can  happen 
only  at  the  new  moon,  or  when  the  moon  at  her  conjunction 
is  near  one  of  her  nodes ;  for  unless  the  moon  is  in  or  near 
one  of  her  nodes,  she  cannot  appear  in  the  same  plane  with 
the  sun,  or  seem  to  pass  over  his  disk.  In  every  other  part 
of  her  orbit  she  will  appear  above  or  below  the  sun.  If  the 
10 


no  ECLIPSES    OP   THE    SUN. 

moon  be  in  one  of  her  nodes,  she  will,  in  most  cases,  cover 
the  whole  disk  of  the  sun  and  produce  a  total  eclipse  ;  if  she 
be  any  where  within  about  sixteen  degrees  of  anode,  b, par- 
tial eclipse  will  be  produced.  When  a  bright  luminous 
ring  appears  round  the  dark  body  of  the  moon  during  an 
eclipse  of  the  sun,  it  is  called  an  annular  eclipse.  This 
kind  of  eclipse  is  occasioned  by  the  moon  being  at  her 
greatest  distance  from  the  earth  at  the  time  of  an  eclipse  ; 
in  which  situation,  the  vertex  or  point  of  the  con,e  of  the 
moon's  shadow  does  not  reach  the  surface  of  the  earth.  A 
total  eclipse  of  the  sun  is  a  very  curious  and  uncommon 
spectacle;  and  total  darkness  cannot  last  more  than  three  or 
four  minutes.  Of  one  tliat  was  observed  in  Portugal  more 
than  one  hundred  and  fifty  years  ago,  it  is  said  that  the 
darkness  was  greater  than  that  of  night ; — that  some  of 
the  largest  stars  made  their  appearance  ; — and  that  birds 
were  so  terrified  that  they  fell  to  the  ground.  A  very  re- 
markable total  eclipse  took  place  in  New  England  June  16, 
1806.  The  day  was  clear ;  several  stars  were  visible;  the 
birds  were  greatly  agitated  ;  and  a  gloom  spread  over  the 
landscape.  The  first  gleam  of  light,  contrasted  with  the 
previous  darkness,  seemed  like  the  usual  meridian  day. 

Questions. — 1,  What  is  an  eclipse  of  the  moon  ?  2.  Describe 
the  earth's  shadow.  3  When  does  an  eclipse  of  the  moon  happen'' 
4.  Why  is  she  not  eclipsed  at  every  full  moon  ?  5.  How  near  a  node 
must  she  be  in  order  to  be  eclipsed  ?  6.  How  long  may  an  eclipse  of 
the  moon  last .''  7.  From  the  knowledge  of  what  circumstances  are 
hmar  eclipses  calculated  ?  8.  Over  what  part  of  the  earth  are  they 
visible.'  9.  What  is  the  cause  of  an  eclipse  of  the  sun.''  ]0.  When 
does  an  eclipse  of  the  sun  happen  ?  11.  Why  can  it  not  happen  at 
other  times  ?  12.  W^hen  will  the  moon  produce  a  total  eclipse  of  the 
sun  .''  13.  Partial .''  14.  When  is  an  eclipse  of  the  sun  called  annu- 
lar .'' — why .''  15.  What  occasions  this  kind  of  eclipses  ?  16.  How 
long  may  a  total  eclipse  of  the  sun  last.''  [Note.  The  diameters  of 
the  sun  and  moon  are  supposed  to  be  divided  into  12  equal  parts,  called 
digits.  They  are  said  to  have  as  many  digits  eclipsed  as  12th  parts 
involved  in  darkness.]  17.  Look  at  fig.  45.  and  illustrate  an  eclipse  of 
the  moon.     18.  At  fig.  44.  and  illustrate  an  ecUpseof  the  tun. 


kARS,  VESTA,  JUNO,  AND  PALLAS.         Ill 


LESSON  50. 

^  Mars,  Vesta,  Juno,  Pallas,  and  Ceres. 

'  JB    Eccen'tric,  deviating  from  the  centre. 
'      Eccentri^'ity,  the  distance  between  the  centre  of  an  ellipse  and 
the  focus. 

Mars,  the  first  of  the  exterior  planets,  is  distinguished 
from  the  rest  by  the  redness  of  its  colour,  which  has  been 
attributed  to  the  density  of  his  atmosphere.  He  revolves 
round  the  sun  in  about  tvv^o  years,  at  the  mean  distance  of 
one  hundred  and  forty-four  millions  of  miles,  and  turns  on 
his  axis  in  a  little  less  than  twenty-five  Piours.  The  time  of 
his  diurnal  rotation  was  discovered  by  means  of  a  large  spot 
seen  on  his  surface,  when  in  that  part  of  his  orbit  which  is 
opposite  to  the  sun  and  the  earth.  The  telescopic  appear- 
ance of  Mars  is  exceedingly  variable ;  but  the  predommant 
brightness  of  his  polar  regions,  leads  to  the  supposition,  that, 
like  those  of  the  earth,  they  are  covered  with  perpetual  snow. 
The  proportion  of  ^sht  and  heat,  received  at  Mars  from 
the  sun,  is  less  than'tDifi  half  of  that  enjoyed  by  the  earth. 

The  planet  next  to  Mars  in  the  solar  system  is  Vesta.  It 
shines  with  a  pure  and  white  light,  and  is  visible  in  a  clear 
evening  without  the  aid  of  a  telescope.  '  It  revolves  round 
the  sun,  in  about  three  years  and  eight  months,  at  the  mean 
distance  of  two  hundred  and  twenty-three  millions  of  miles. 
Vesta  was  first  discovered  by  Dr.  Oibers,  of  Bremen,  in 
Lower  Saxony,  March  29,  1807. 

Juno  was  discovered  by  Mr.  Harding,  near  Bremen,  Sep- 
tember 1,  1804.  It  completes  its  revolution  in  about  four 
years  and  four  months,  at  a  mean  distance  from  the  sun  of 
about  two  hundred  and  fifty-three  millions  of  miles.  It  is 
distinguished  from  all  the  other  planets  by  the  great  eccen- 
tricity .of  its  orbit ;  and  the  effect  of  this  is  such  that  it 
passes  over  one  half  of  its  orbit  in  half  the  time  that  it  em- 
ploys in  describing  the  other  half.  From  the  same  cause  its 
greatest  distance  from  the  sun  is  double  the  least  distance, 
the  difference  between  the  two  distances  being  about  one 
hundred  and  twenty-seven  millions  of  miles. 

Pallas  was  discovered  by  Dr.  Oibers,  March  28,  1802.  It 
completes  its  revolution  in  about  four  years  and  seven  months, 
and  its  orbit  is  nearly  as  eccentric  as  that  of  Juno.     Its  mean 


113                                                     CERES.  % 

distance  from  the  sun  is  two  hundred  and  sixty-three  millions  | 

of  miies.     Its  atmosphere  seems  to  be  dense  and  cloudy.  I 

The  planet  Ceres  was  discovered  by  Piazzi,  at  Palermo,  i 

in  Sicily,  January  1,  1801.     It  is  apparently  surrounded  by  ■ 

a  dense  atmosphere,   and  is  of  a  ruddy  appearance.     Its  j 

mean  distance  from  the  sun,  and  its  revolution  in  its  orbit  is  i 

nearly  the  same  as  that  of  Pallas.     These  newly  discovered  ^ 

planets  exhibit  various  changes  in  appearance  and  size ;  so  j 

that  their  real  magnitude  has  not  been  ascertained  with  cer-  ; 

tainty.  '*^ 

From  some  irregularities,  observed  in  the  motions  of  the  "J 

old  planets,  some  astronomers  had  been  led  to  suppose,  long  ^ 

before  the  discovery  of  the  four  new  planets,  that  a  planet  < 

existed  between  the  orbits  of  Mars  and  Jupiter.    Dr.  Olbers,  j 

before  he  made   his   last  discovery,  conceived   that   these  '■ 

small  celestial  bodies  were  merely  the  fragments  of  a  larger  j 

planet,  which  had  been  burst  asunder  by  some  internal  con-  ; 

vulsion,  and  that  several  more  might  be  discovered.     With  .: 

the  intention,  therefore,  of  detecting  other  fragments  of  the  j 

supposed  planet,   he  examined,  thriopoowery  year,  the  little  J 

stars  in  certain  constellations,  till  hi^iabours  were  crowned  ^ 

with  success  by  the  discovery  of  the  new  planet  Vesta.    The  t 

opinion,  that  these  four  small  planets  have  been  separated  \ 

from  one  original  planet,  by  some  convulsion  in  nature,  has  1 

been  maintained  by  Dr.  Brewster  with  much  ingenuity  and  j 

plausibility.     He  supposes,  moreover,  that  the  phenomena  ] 

of  the  meteoric  stones,  whicli  have  fallen  on  the  earth  from  \ 

the  atmosphere,  may  have  been  occasioned  by  the  bursting  j 

of  this  planet.  1 

Questions. — 1.  By  what  is  Mars  distinguished  from  the  rest  of  ; 
the  planets  ?  2.  Tn  what  time  does  Mars  revolve  round  the  sun  ?  3.  ', 
At  what  mean  distance  f  4.  What  is  the  time  of  his  diurnal  rotation,  i 
and  how  was  it  discovered  ?  5.  What  is  the  telescopic  appearance  | 
of  Mars  ?  6.  Proportion  of  light  and  heat  ?  7.  What  is  the  appear- 
ance of  Vesta  ?  8.  When,  where,  and  by  whom  were  each  of  the  i 
new  planets  discovered  ?  9.  What  is  the  distance  of  each  from  the  j 
sun  .''  10.  By  what  is  Juno  distinguislied  from  all  the  other  planets?  < 
11.  What  supposition  did  some  astronomers  make  before  the  discoverj  ' 
of  the  new  planets  ?  12.  What  was  the  conjecture  of  Dr.  Olbers, 
and  to  what  did  it  lead  ?  13.  To  what  does  Dr.  Brewster  think  the  ; 
phenomena  of  meteoric  stones  may  be  attributed  .-'  i 


JUPITER.  115 

LESSON  51. 

Jupiter. 

J  jpiTER  is  the  largest  of  all  the  planets.  His  diameter  is 
eighty-nine  thousand  miles.  He  revolves  round  the  sun  at 
the  mean  distance  of  four  hundred  and  ninety  millions  of 
miles,  completes  a  revolution  in  a  little  less  than  twelve  years, 
and  turns  on  his  axis  in  the  short  interval  of  nine  hours' and 
fifty-six  minutes.  With  the  exception  of  Venus,  Jupiter  is 
the^  most  brilliant  of  the  planets,  and,  when  viewed  through 
a  telescope,  its  surface  is  remarkable  for  being  always  co- 
vered with  a  number  of  belts  or  stripes  of  various  shades. 
They  are  not  regular  or  constant  in  their  appearance,  and 
their  breadth  is  also  variable,  one  belt  growing  narrower 
while  another  in  its  neighbourhood  becomes  broader,  as  if 
one  had  flowed  into  the  other.  Sometimes  one  or  more  spots 
are  formed  between  the  belts,  which  increase  until  the  whole 
are  united  in  one  large  dusky  band.  Bright  spots  also  may 
be  discovered  on  Jupiter's  surface,  which  are  more  perma- 
nent than  the  belts,  and  re-appear  after  unequal  intervals  of 
time.  For  the  cause  of  these  appearances,  we  are  referred 
by  eminent  philosophers,  to  his  swift  diurnal  motion,  to  the 
changes  in  the  density  of  his  atmosphere,  as  occasioned  by 
variations  of  temperature,  and  to  other  incidental  agencies. 
The  axis  of  Jupiter  is  perpendicular  to  the  plane  of  his  orbit ; 
his  inhabitants,  therefore,  will  experience  no  change  of  sea- 
sons, nor  difference  in  the  length  of  their  days  and  nights. 
At  the  equator  there  will  be  perpetual  summer,  and  at  the 
poles  unceasing  winter.  The  degree  of  light  and  heat  is 
about  twenty-five  times  less  than  at  the  earth. 

The  satellites  of  Jupiter  are  invisible  to  the  naked  eye, 
but  through  a  telescope  they  make  a  beautiful  appearance. 
As  our  moon  turns  round  the  earth,  enlightening  the  nights 
by  reflecting  the  rays  of  the  sun,  so  these  also  enlighten  the 
nights  of  Jupiter,  and  move  round  him  in  different  periods 
of  time,  proportioned  to  their  several  distances.  They  often 
pass  behind  the  body  of  the  planet,  and  also  into  its  shadow, 
and  are  eclipsed.  These  eclipses  are  of  use  for  ascertaining 
the  longitude  of  places.  They  have  led  to  the  discovery, 
that  light  is  about  eight  minutes  in  coming  from  the  sun  ta 
10* 


114  SATURN. 

the  earth ;  for  an  eclipse  of  one  of  these  satellites  appears 
to  us  to  take  place  sixteen  minutes  sooner,  when  the 
earth  is  in  the  part  of  her  orbit  nearest  Jupiter,  than  when 
in  the  part  farthest  from  him.  Hence  light  is  sixteen  minutes 
in  crossing  the  earth's  orbit,  and  of  course  eight  minutes  in 
coming  from  the  sun.  An  observer  on  Jupiter,  with  eyes 
constructed  like  ours,  could  never  see  Mercury,  Venus,  the 
Earth,  or  Mars,  for,  on  account  of  the  immense  distance, 
they  are  always  immersed  in  the  sun's  rays. 

QcTESTiONS. — 1.  What  is  the  diameter  of  Jupiter  ? — distance  from 
the  sun  P — time  of  revolution  round  the  sun  ? — diurnal  rotation  ?  2 
Describe  the  telescopic  appearance  of  Jupiter.  3.  What  is  the  posi* 
tion  of  his  axis,  and  the  consequence  of  that  position  ?  4.  What  a 
said  of  Jupiter's  moons  ?  5.  Of  what  use  are  their  eclipses  ?  C.  To 
w^hat  discovery  have  they  led  ? — how  ? 


LESSON  52. 

Saturn  and  Uranus. 

Anoni'aly,  irregularity,  deviation  from  rule. 

Hypoth'esis,  a  supposition,  a  system  formed  under  some  principle 
not  proved. 

Saturn  though  not  so  brilliant  as  Jupiter,  is  a  very  con- 
spicuous planet.  It  shines  with  a  pale  light,  and  the  degree 
of  heat  and  light  is  eighty  times  less  than  at  the  earth.  It 
revolves  round  the  sun  in  little  less  than  thirty  years,  at  the 
mean  distance  of  nine  hundred  millions  of  miles.  It  turns 
on  its  axis  in  little  more  than  ten  hours,  and  its  diameter  is 
seventy-nine  thousand  miles. 

Saturn,  as  seen  through  a  good  telescope,  is  a  beautifu. 
object,  having  seven  moons,  a  double  ring,  and  appearances 
similar  to  the  belts  of  Jupiter.  The  ring  is  one  of  the 
greatest  anomalies  in  our  system.  It  is  a  thin,  broad,  opaque, 
circular  body,  encompassing  the  planet  without  touching  it, 
like  the  wooden  horizon  of  an  artificial  globe.  Although 
the  phenomenon  is  usually  termed  the  ring,  yet  it  consists. 
of  two,  entirely  detached  from  each  otV.er  and  from  the  body 
of  the  planet,  one  exactly  without  or  beyond  the  other. 
Stars  have  been  seen  through  the  vacancy  between  them, 
and  also  .between  the  inner  ring  and  the  planet.     Concern; 


ni 


COMETS.  115 

ing  the  nature  and  uses  of  the  ring  there  have  been  various 
hypotheses.  Dr.  Herschel  thinks  it  not  less  solid  than  the 
body  of  Saturn  itself,  and  it  is  observed  to  cast  a  strong 
shadow  upon  it.  The  light  of  the  ring  is  generally  brighter 
than  that  of  the  planet,  which  has  been  attributed  to  its  si- 
tuation above  the  region  of  mists  and  clouds.  Both  the  pla- 
net and  the  ring  perform  their  rotations  about  the  same  com- 
mon axis,  and  in  nearly  the  same  time.  The  ring  disappears 
twice  in  every  revolution  of  the  planet  round  the  sun  ;  that 
is,  once  in  fifteen  years,  and  Saturn  appears  quite  circular 
for  nine  months  together.  Some  have  supposed  that  the  use 
of  the  ring  is  to  collect,  refract,  and  transmit  the  rays  of  tlig 
sun  to  the  body  of  the  planets 

The  planet  Uranus,  or  Herschel,  completes  a  revolution 
round  the  sun  in  about  eighty-four  years.  On  account  of 
its  distance  from  the  earth,  which  is  eighteen  hundred  mil- 
lions of  miles,  its  diurnal  rotation  has  never  been  determined. 
Heat  and  light  at  Uranus  are  about  three  hundred  and  sixty 
times  less  than  at  the  earth.  It  is  scarcely  visible  to  the 
naked  eye,  although  its  diameter  is  thirty-five  thousand  miles. 
Astronomers  formerly  considered  it  as  a  star,  but  on  the  13th 
of  March,  1781,  Dr.  Herschel  discovered  it  to  be  a  planet. 

Qltestions. — 1.  How  far  is  Saturn  from  the  sun?  2.  What  de- 
gree of  light  and  heat  has  it  ?  3.  How  often  does  it  revolve  round  the 
sun  ?  4.  On  its  ov/n  axis  ?  5.  What  is  the  appearance  of  Saturn  as 
seen  through  a  telescope  ?  6.  Describe  the  ring.  7.  What  is  said  con- 
cerning the  nature  and  uses  of  the  ring.  8.  In  what  time  does  Ura- 
nus complete  a  revolution  ?  9.  At  what  distance  from  the  sun  .''  10. 
What  is  the  diameter  of  Uranus  ?  11.  Degree  of  heat  and  light  ?  12^. 
When  and  by  whom  discovered.-'  [Note.  Saturn's  inner  ring  is  dis- 
tant from  its  body  21,100  miles.  The  breadth  of  the  inner  ring  is 
20,000  miles.  The  outer  ring  is  distant  from  the  inner  ring  2,839 
miles,  and  the  breadth  of  the  outer  ring  is  7,200  miles.  Uranus  is  the 
name  which  has  been  given  to  the  planet  Herschel,  or  Georgium  Si- 
dus,  on  the  continent  of  Europe.} 


LESSON  53. 

Comets. 

Hast  thou  ne'er  seen  the  comet's  flaming  flight  ? 
Th'  illustrious  stranger  passing,  terror  sheds 


116  COMETS. 

On  gazing  nations,  from  his  fiery  train 
Of  length  enormous ;  takes  his  ample  round 
Through  depths  of  ether ;  coasts  unnumbered  WOflds 
Of  more  than  solar  glory  ;  doubles  wide  -^ 

Heaven's  mighty  cape,  and  then  revisits  earth, 
From  the  long  travel  of  a  thousand  years.       Young. 
Besides  the  primary  and  secondary  planets,  there  are  other   ] 
bodies  which  revolve  round  the  sun,  and  consequently  make    • 
apart  of  the  solar  system.     These  are  called  comets,  and   i 
appear  occasionally  in  every  part  of  the  heavens.     They  are 
solid,  opaque  bodies,  generally  distinguished  by  a  lucid  train    i 
or  tail,  issuing  from  that  side  which  is  turned  away  from  the  I 
sun.     Most  of  them  move  in  very  elliptical  orbits ;  at  one  J 
time  coming  very  near  the  sun,  even  nearer  than  Mercury,  ■] 
and  again   receding  to  a  distance  far  beyond  the  orbit  of  ^i 
Uranus.    The  train  is  so  transparent,  that  the  fixed  stars  may  ^ 
be  seen  through  it,  and  sometimes  it  extends  to  an  immense  J 
distance  in  the  heavens.   The  farther  it  reaches,  the  broader    1 
it  seems  to  become,  and  at  times  it  is  divided  into  rays.  ■ 

Viewed  through  a  telescope,  comets  appear  full  of  spots 
and  inequalities,  and  a  vapour  frequently  renders  it  impos-  , 
sible  to  observe  their  figure.  In  a  clear  sky,  however,  the  | 
solid  body  of  a  comet  oTten  reflects  a  splendid  light.  That  i 
part  of  astronomy  relating  to  comets  is  still  imperfect,  for  the  ^ 
opinion  once  prevailed,  that  they  were  only  meteors  gene-  i 
rated  in  the  air,  like  those  we  see  in  a  clear  night,  vanishing  * 
in  a  few  moments,  and  no  care  therefore  was  taken  to  ob-  "i 
serve  or  record  their  phenomena  with  accuracy.  .| 

The  number  of  comets  belonging  to  the  solar  system  is  | 
unknown.  More  than  five  hundred  have  appeared  since  the  ^ 
commencement  of  the  christian  era.  The  orbits  of  ninety- 
eight  comets,  up  to  the  year  1808,  have  been  calculated  j 
but  of  all  the  comets  the  periods  of  only  three  are  known 
with  any  degree  of  certainty,  being  found  to  return  at  inter- 
vals of  seventy-five,  one  hundred  twenty-nine,  and  five  hun- 
dred and  seventy-five  years  ;  and  of  these  that  which  appear- 
ed in  1680  is  the  most  remarkable.  This  comet,  which  will 
not  appear  again  till  the  year  2225,  at  its  greatest  distance, 
is  about  eleven  thousand  two  hundred  millions  of  miles  from 
the  sun,  while  its  least  distance  from  the  centre  of  the  sun  is 
about  four  hundred  ninety  thousand  miles.  In  that  part  of 
its  orbit  nearest  the  sun,  it  flies,  according  to  Newton,  with 


THE    FIXED    STARS.  117 

a  velocity  of  eight  hundred  eighty  thousand  miles  an  hour ; 
but  according  to  calculations  made  since  the  days  of  New- 
ton, its  motion  has  been  computed  to  be  one  million  two 
hundred  forty  miles  an  hoar. 

The  comet  of  1758  was  looked  for  with  great  interest  by 
astronomers,  because  its  return  had  been  predicted.  But  it 
is  worthy  of  remark,  that  what,  in  this  century,  excited  only 
the  curiosity  of  astronomers  and  mathematicians,  had  been 
regarded  four  revolutions  before,  in  1456,  with  feelings  of 
horror.  Its  long  train  spread  consternation  over  all  Europ6, 
already  terrified  at  the  success  of  the  Turkish  arms,  which 
had  just  destroyed  the  great  empire.  Pope  Callixtus,  on  this 
occasion,  ordered  a  prayer,  in  which  the  comet  and  the 
Turks  were  included  in  the  same  anathema. 

Questions. — 1.  What  are  comets  ?  2.  How  do  they  move  ?  3. 
What  is  said  of  the  train  of  a  comet?  4.  How  do  comets  appear 
through  a  telescope  ?  5.  Wliat  is  said  of  the  number  of  comets  ?  6. 
What  is  known  of  the  orbits  of  cornets  ?  7.  What  is  said  of  the  comet 
of  1680  ?  8.  What  is  worthy  of  remark  with  respect  to  the  comet  of 
1758.'     [Note.  The  comet  of  1758  is  expected  to  return  in  1834.] 


LESSON  54. 

The  Fixed  Stars. 

Neb'ula,  (plural,  nebula?,)  a  cloud  of  obscure  light  in  the  heavens ; 
some  nebulae  consist  of  clusters  of  telescopic  stars,  others  ap- 
pear as  luminous  spots  of  different  forms.    Sir'ius,  the  dog-star. 

Those  luminous  bodies  which  always  appear  in  the  hea- 
vens at  the  same  distance  from  each  other,  are  called  fixed 
stars ;  because,  with  the  exception  of  a  few,  which,  in  a 
course  of  years,  appear  to  change  their  places,  it  has  not 
been  discovered,  that  they  have  any  proper  motion  of  their 
own.  When  viewed  through  a  telescope  they  appear  as 
points  of  small  magnitude  ;  they  must  be  at  such  an  immense 
distance,  therefore,  as  to  be  invisible  to  the  naked  eye,  if 
they  borrowed  their  light ;  as  is  the  case  with  the  satellites 
of  Jupiter  and  Saturn,  although  they  appear  of  very  distin- 
guishable magnitu4e  through  a  telescope.  The  stars  are 
probably  suns,  around  each  of  which  revolve  primary  and 
secondary  planets,  as  about  our  sun.  They  are  distinguish- 
able from  the  planets  by  their  twinkling. 


118  THE  MILKY  WAY.  j 

The  magnitudes  of  the  fixed  stars  appear  to  be  different    ' 
from  one  anotlier,  which  difference  may  arise  either  from  a    j 
diversity  in  their  real  magnitudes,    or  distances;  or  from 
both  these  causes  acting  together.     The  difference  in  the 
apparent  magnitude  of  the  stars  is  such  as  to  admit  of  their    i 
being  divided  into  six  classes,  the  largest  being  called  stars   I 
of  the  first  magnitude,  and  the  least  which  are  visible  to  the  ^ 
naked  eye,  stars  of  the  sixth  magnitude.     Stars  that  cannot   '\ 
be  seen  without  the   help  of  glasses  are  called  telescopic   '■ 
stars.     The  number  of  stars,  visible  at  any  one  time  to  the 
naked  eye,  is  about  one  thousand ;  but  Dr.  Herschel,  by  his  i 
skilful  improvements  of  the  reflecting  telescope,  has  disco-  | 
vered  that  the  whole  number  is  great  beyond  all  conception.  J 
Upon  viewing  the  heavens  during  a  clear  night,  we  discover  % 
a  pale  irregular  light,  and  a  number  of  stars  whose  mingled 
rays  form  the  luminous  tract  called  the  milky-way.     The   j 
stars  themselves  are  at  too  great  a  distance  to  be  perceived    ] 
by  the  naked  eye ;  and  among  those  which  are  visible  with    ■ 
a  telescope  there  are  spaces  apparently  filled  with  others  in 
immense  numbers.     Many  whitish  spots  or  tracts  (called 
nehuloi)  are  visible  in  different  parts  of  the  heavens,  which  ^. 
are  supposed  to  be  milky-ways  at  an  inconceivable  distance.   ] 

The  distance  of  these  remoter  bodies  is  so  vast  and  mea-    i 
sureless,  that  we  can  hardly  speak  of  it  except  in  relation  to    i 
the  inconceivable  swiftness  of  light.     The  rays  by  which    ^^ 
they  are  now  made  visible  to  the  eye  of  the  astronomer,    k 
the  rapid  motion  of  which  might  circle  the  earth  while  on«    \ 
is    pronouncing  a  syllable,  have   been  darting  forward  for    1 
thousands  and  ten  thousands  of  years  to  reach  us.     All  the  I 
events  and  revolutions,  which  history  records,  have  taken 
place  during  their  progress.     They  commenced  their  career, 
it  has  been  computed,  at  a  period  of  such  remote  antiquity, 
that,  compared  with  it,  the  date  of  that  time,  when  God 
gave  the  earth  to  man  for  a  habitation,  is  but  of  yesterday. 

Dr.  Herschel  has  calculated  that  the  distance  of  the  re- 
motest nebulae,  exceeds  that  of  the  nearest  fixed  star  at  least 
three  hundred  thousand  times.  Upon  this  fact,  he  thus  re- 
marks ;  a  telescope  with  a  power  of  penetrating  into  space, 
like  my  forty  feet  one,  has  also,  as  it  may  be  called,  a 
power  of  penetrating  into  time  past.  To  explain  this  we 
must  consider  that  from  the  known  velocity  of  light,  it  may 
be  proved  that  when  we  look  at  the  star  called  Sirius,  the 


THE    CONSTELLATIONS.  119 

rays  which  enter  the  eye  cannot  have  been  less  than  six 
years  and  four  months  and  a  half  coming  from  that  star  to 
the  observer.  Henceit  follows  that  when  we  see  an  object 
at  the  calculated  distance,  at  which  one  of  these  very  remote 
nebulae  may  still  be  perceived,  the  rays  of  light  which  con- 
vey its  image  to  the  eye,  must  have  been  more  than  nineteen 
hundred  and  ten  thousand,  that  is,  almost  two  millions  of 
years  on  their  way ;  and  that,  consequently,  so  many  years 
ago,  this  object  must  already  have  had  an  existence  in  the 
sidereal  heavens,  in  order  to  send  out  those  rays  by  which 
we  now  perceive  it. 

But  when  we  have  reached  the  utmost  distance  to  which 
the  power  of  our  instruments  can  penetrate,  who  will  say, 
that  we  are  approaching  any  limits  of  the  creation  1  who 
will  say,  that  if  the  disembodied  spirit  should  travel  forward 
through  eternity,  numberless  systems  would  not  be  continual- 
ly spreading  before  it  ?  All  that  part  of  the  universe  which 
we  are  able  to  discern,  is  peopled  by  inhabitants,  who  have 
the  common  want  of  heat  and  light ;  who  will  say,  that 
there  are  not  other  parts  of  the  material  universe  inhabited 
by  beings  of  different  natures,  to  whom  these  wants  are  un- 
known ?  It  is  only  some  pontion,  we  know  not  how  small, 
of  the  material  universe  which  is  obvious  to  our  senses ; 
who  will  attempt  to  define  the  limits  of  the  invisible  world  ? 
who  will  attempt  to  set  bounds  to  the  works  of  infinite  power 
and  infinite  goodness? 

Questions. — 1.  What  are  fixed  stars? — why  so  called?  2.  How 
docs  it  appear  that  they  do  not  borrow  their  light  ?  3.  What  is  said 
of  the  magnitude  of  the  stars  ?  4.  Number?  5.  Describe  the  milky- 
way  (or  galaxy.)  6.  What  calculations  did  Dr.  Herschel  make  ? 
[Note.  Many  stars,  single  to  the  naked  eye,  appear  double,  triple, 
and  even  quadruple,  through  a  telescope.  Dr.  Herschel  found  that  in 
more  than  fifty  double  stars,  a  change  of  situation  really  takes  place  • 
it  is  concluded,  therefore,  that  they  describe  orbits  round  a  centre  of 
gravity.] 


LESSON  55 

The  Constellations 

The  first  people  who  paid  much   attention  to  the  fixed 
stars  were  the  shepherds  in  the  beautiful  plains  of  Egypt 


120  THE    CONSTELLATIONS.  \ 

\ 

and  Babylon.  Endowed  with  a  lively  fancy,  they  divided  i 
the  stars  into  different  companies  or  constellations,  each  of  ^ 
which  they  supposed  to  represent  the  -image  of  some  animal,  | 
or  other  terrestrial  object.  Of  these  ancient  constellations 
there  were  fifty,  to  which  the  moderns  have  added  about  ^ 
thirty  others.  Twelve  of  these  constellations  are  in  the  zo-  ; 
diac,  bearing  the  same  names  with  the  signs  of  the  zodiac  j 
or  ecliptic.  But  these  constellations  and  signs  do  not  coin-  ; 
cide,  for  the  equinoctial  points  are  not  stationary,  but  move  i 
backward,  and  the  sign  Aries  always  begins  at  one  of  them, 
and  all  the  other  signs  each  succeed  Aries  in  order  ;  it  fol-  , 
lows  therefore  that  all  the  signs  of  the  ecliptic  or  zodiac  J 
move  backward  with  the  equinoxes.  The  distance  which  ; 
they  move  annually  is  about  fifty  seconds  of  a  degree ;  so  i 
that  with  respect  to  the  fixed  stars  the  equinoctial  points  fall  | 
backwards  thirty  degrees,  in  about  two  thousand  two  hun-  ; 
dred  years,  whence  the  stars  will  appear  to  have  gone  for-  '■■ 
ward  thirty  degrees,  with  respect  to  the  signs  of  the  ecliptic,  ^ 
which  are  always  reckoned  from  the  equinoctial  points,  j 
This  shows  the  importance  of  distinguishing  between  the 
signs  of  the  zodiac  and  the  constellations  of  the  zodiac  ;  for  ^ 
stars,  which  are  in  one  sign  at  one  time,  will  be  in  the  sue-  i 
ceeding  one  at  another.  Thus,  the  stars  which  were  for-  i 
merly  in  Aries,  are  now  in  Taurus,  and  so  on.  When  these  j 
names  were  given  to  the  signs  and  constellations,  it  is  sup-  i 
posed  that  each  sign  coincided  with  the  constellation  of  the  I 
same  name  ;  but  on  account  of  this  moving  of  the  equinoc-  \ 
tial  points,  or,  as  it  is  termed,  the  precession  of  the  equinoxes,  - 
there  is  now  about  one  sign  or  thirty  degrees  difference. 
The  period  will  be  completed  in  about  twenty-six  thousand 
years. 

Among  the  northern  constellations,  none  are  more  re- 
markable than  that  which  is  nearest  to  the  north  pole,  and 
termed  the  little  bear.  The  last  star  of  its  tail  is  but  two  de- 
grees from  the  pole  ;  hence  it  is  called  the  polar  star.  It  is  | 
easily  distinguished  from  the  neighbouring  stars,  because  it 
scarcely  appears  to  change  its  position,  and  is  ahvays  in  the 
same  part  of  the  heavens.  By  its  fixed  situation  it  becomes 
a  guide  to  travellers,  and  particularly  to  mariners  who  are 
sailing  on  the  open  seas.  Before  the  discovery  of  the  com- 
pass sailors  had  no  surer  guide  than  the  polar  star ;  and 
even  now,  when  the  sky  is  serene,  they  repose  in  many  cases 


HYMN  TO  THE  NORTH  STAR.  121 

with  greater  certainty  upon  the  direction  of  this  star,  than 
upon  the  magnetic  needle. 

Hymn  to  the  North  Star. 

The  sad  and  solemn  night 
Has  yet  her  multitude  of  cheerful  fires  ; 

The  glorious  host  of  light 
Walk  the  dark  hemisphere  till  she  retires : 
All  through  her  silent  watches  gliding  slow, 
Her  constellations  come,  and  round  the  heavens,  and  go. 

Day,  too,  hath  many  a  star 
To  grace  his  gorgeous  reign,  as  bright  as  they : 

Through  the  blue  fields  afar, 
Unseen,  they  follow  in  his  flaming  way. 
Many  a  bright  lingerer,  as  the  eve  grows  dim. 
Tells  what  a  radiant  troop  arose  and  set  with  him. 

And  thou  dost  see  them  rise, 
Star  of  the  Pole !  and  thou  dost  see  them  set. 

Alone  in  thy  cold  skies, 
Thou  keep'st  thy  old  unmoving  station  yet, 
Nor  join'st  the  dances  of  that  glittering  train, 
Nor  dip'st  thy  virgin  orb  in  the  blue  western  main 

There,  at  morn's  rosy  birth. 
Thou  lookest  meekly  through  the  kindling  air. 

And  eve,  that  round  the  earth 
Chases  the  day,  beholds  thee  watching  there  ; 
There  noontide  finds  thee,  and  the  hour  that  calls 
The  shapes  of  polar  flame  to  scale  heaven's  azure  walls 

On  thy  unaltering  blaze 
The  half-wrecked  mariner,  his  compass  lost, 

Fixes  his  steady  gaze, 
And  steers,  undoubting,  to  the  friendly  coast  ; 
And  they  who  stray  in  perilous  wastes,  by  night. 
Are  glad  when  thou  dost  shine  to  guide  their  footsteps 
right. 

And,  therefore,  bards  of  old. 
Sages,  and  hermits  of  the  solemn  wood 

Did  in  thy  beams  behold 
A  beauteous  type  of  that  unchanging  good, 
11 


1^  FORMS    AND   DIVISIONS    OF   TIME. 

That  bright  eternal  beacon,  by  whose  ray 
The  voyager  of  time  should  shape  his  heedful  way. 

Bryant. 

Questions. — 1.  What  is  said  of  the  first  division  of  the  stars  into 
constellations  ?  2.  Why  do  not  the  constellations  and  signs  of  the 
zodiac  coincide  ?  3.  What  is  the  present  difference  between  them  ? 
4.  At  what  rate  does  the  change  take  place  ?  5.  Describe  tne  situa- 
tion of  the  polar  star. 


LESSON  56.  <: 

Forms  and  Divisions  of  Time.  \ 

As  the  form  of  the  year  is  various  among  different  na-  -\ 
tions,  so  is  its  beginning,  llie  Jews,  like  most  other  na-  ; 
tions  of  the  East,  had  a  civil  year,  which  commenced  with 
the  new  moon  in  September;  and  an  ecclesiastical  year,  ■ 
which  commenced  from  the  new  moon  in  March.  The  \ 
Persians  besrin  their  year  in  the  month  answering  to  our 
June  ;  the  Chinese,  and  most  of  the  inhabitants  of  India,  ] 
begin  it  with  the  first  moon  in  March  ;  and  the  Greeks  with  :; 
the  new  moon  that  follows  the  longest  day.  In  England  and  \ 
America,  the  civil  or  legal  year  formerly  commenced  on  the  ' 
twenty-fifth  of  March,  and  the  historical  year  on  the  first  of  * 
January.  But  since  the  alteration  of  the  style,  which  took  '■- 
place  in  1752,  the  civil  year  in  both  countries  has  likewise  | 
begun  on  the  first  of  January.  I 

The  principal  division  of  the  year  is  into  parts  called   j 
months,  which  are  either  astronomical  or  civil.     An  astrono- 
mical or  natural  month  is  that  which  is  measured  exactly   : 
by  the  motion  of  the  Earth  or  Moon,  and  is  accordingly   ] 
either  lunar  or  solar.     A  lunar  month  is  the  time  the  moon  ] 
takes  to  revolve  round  the  earth,  which  she  performs  in   \ 
twenty-seven  days,  seven  hours,  and  forty-three  minutes.     A   ; 
solar  month  is  that  space  of  time  in  which  the  earth  runs 
through  one  of  the  signs  of  the  zodiac  ;  as  the  earth  con-  1 
stantly  travels  through  the  twelve  signs  in  three   hundred  j 
and  sixty-five  days  five  hours  and  forty-nine  minutes,  each 
solar  month  is  found  by  dividing  this  number  by  twelve,  to  ■ 
contain  thirty  days,  ten  hours,  and  twenty-nine  minutes,  j 


EQUATION    OP   TIME.  123 

Civil  months  are  those  which  are  framed  to  serve  the  uses 
of  life,  and  approach  nearly  to  the  quantity  of  astronomical 
months  either  lunar  or  solar ;  being  made,  with  the  excep- 
tion of  February,  to  consist  of  thirty  and  thirty-one  days. 
To  the  days  of  a  week,  the  Pagans  gave  the  names  of  the 
sun,  moon,  and  planets  ;  and  for  the  first  two  days  and  last 
day  of  our  weeks,  those  names  are  still  retained. 

A  natural  or  solar  day  is  the  time  which  the  sun  takes  in 
passing  from  the  meridian  of  any  place  till  it  comes  round 
to  the  same  meridian  again ;  or  it  is  the  time  from  noon  to 
noon.  A  sidereal  day  is  the'time  in  which  the  earth  revolves 
once  about  its  axis.  The  rotation  of  the  earth  is  the  most 
equable  and  uniform  motion  in  nature,  and  is  completed 
in  twenty-three  hours,  fifty-six  minutes,  and  four  seconds, 
for  any  meridian  on  the  earth  will  revolve  from  a  fixed  star, 
to  that  star  again  in  this  time.  Sidereal  days,  therefore, 
are  all  of  the  same  length  ;  but  solar  or  natural  days  are  not. 
The  mean  length  of  a  solar  day  is  twenty-four  hours,  but  it 
is  sometimes  a  little  more,  and  sometimes  less.  The  reason 
of  the  difference  between  the  solar  and  sidereal  day  is,  that 
as  the  earth  advances  almost  a  degree  eastward  in  its  orbit, 
in  the  same  time  that  it  turns  eastward  round  its  axis,  it 
must  make  more  than  a  complete  rotation  before  it  can  come 
into  the  same  position  with  the  sun  that  it  had  the  day  be- 
fore ;  in  the  same  way,  as  when  both  the  hands  of  a  watch 
or  clock  set  off  together,  as  at  twelve  o'clock,  for  instance, 
the  minute  hand  must  travel  more  than  a  whole  circle  before 
it  will  overtake  the  hour  hand,  that  is,  before  they  will  be 
in  the  same  relative  position  again.  It  is  on  this  account 
that  the  sidereal  days  are  found  to  be,  on  an  average,  shorter 
than  the  solar  ones  by  three  minutes  and  fifty-six  seconds. 

As  a  clock  is  intended  to  measure  exactly  twenty-four 
hours,  it  is  evident  that,  when  a  solar  day  consists  of  more 
than  twenty-four  hours,  it  will  not  be  noon  by  the  sun  till  it 
is  past  noon  by  the  clock  ;  in  which  case  the  sun  is  said  to 
l)e  slow  of  the  clock.  But  when  a  solar  day  consists  of  less 
than  twenty-four  hours,  it  will  be  noon  by  the  sun  before  it 
is  noon  by  the  clock  ;  and  the  sun  is  then  said  to  be  fast  of 
the  clock.  Time  measured  by  a  clock  is  called  equal  or 
mean  time,  and  that  measured  by  the  apparent  motion  of  the 
sun  in  the  heavens,  or  by  a  sun-dial,  is  called  apparent  time. 
The  adjustment  of  the  difference  of  time,  as  shown  by  a 


J 24  EQUATION    OF   TIME. 

well-regulated  clock  and  a  true  sun-dial  is  called  the  equa* 
tiofi  of  time. 

Since  the  stars  are  found  to  gain  three  minutes  and  fifty-six 
seconds  upon  the  sun  every  day,  amounting  in  a  year  to  one 
diurnal  revolution,  it  follows  that,  in  three  hundred  and  six- 
ty-five days  as  measured  by  the  sun,  there  are  three  hundred 
and  sixty-six  days  as  measured  by  the  stars.  This  regular 
return  of  the  fixed  stars  to  the  meridian  affords  an  easy 
method  of  determining  vi'hether  our  clocks  and  watches  keep 
true  time.  For  if  through  a  small  hole  in  a  window-shutter, 
or  in  a  thin  plate  of  metal  fixed  for  that  purpose,  it  be  ob- 
served at  what  time  any  star  disappears  behind  a  chimney 
or  the  corner  of  a  building  at  a  small  distance ;  then  if  the 
star  disappears  the  next  night  three  minutes  and  fifty-six 
seconds  sooner  by  the  clock  or  watch  than  it  did  the  night 
before,  on  the  second  night  seven  minutes  fifty-two  seconds 
sooner,  and  so  on,  it  is  a  certain  sign  that  the  machine  goes 
right ;  but  if  it  does  not  observe  this  rule,  it  is  evidently  not 
accurate,  and  as  the  disappearing  of  a  star  is  instantaneous, 
we  may  depend  upon  this  information  to  half  a  second  at 
most. 

Questions. — 1.  What  is  said  of  the  form  and  commencement  of 
the  year  among  different  nations  ?  2.  What  is  an  astronomical  month  ? 
3.  Lunar  month  ?  4.  Solar  month  ?  5.  Civil  month  ?  6.  Solar  day  ? 
7.  Sidereal  day  ?  8.  How  does  it  appear  that  sidereal  days  are  all  of 
the  same  length  ?  9.  Why  is  there  a  difference  between  the  lengths 
of  a  solar  and  sidereal  day  ?  10.  When  is  the  sun  said  to  be  slow  of 
the  clock  ?  11.  Fast  of  the  clock  ?  12.  What  is  mean  time  ?  13. 
Apparent  time  ?  14.  Equation  of  time  .^  15.  What  follows  incon- 
sequence of  the  stars  gaining  upon  the  sun  ?  16.  What  is  an  easy 
method  of  determining  whether  clocks  and  watches  keep  true  time  ? 
[Note.  The  inequality  of  solar  days,  as  caused  by  the  eccentricity 
of  the  earth's  orbit,  and  the  obliquity  of  the  ecliptic,  is  clearly  illustrat- 
ed in  Wilkins' Elements  of  Astronomy  :  the  work  has  been  recom- 
mended as  containing  a  judicious  selection  and  concise  statement  of 
the  leading  facts  and  principles  of  the  science.] 


THE  PLANETARY  SYSTEM.  135 

LESSON  57. 

The  Planetary  System. 

Fair  star  of  eve,  thy  lucid  ray 
Directs  my  thoughts  to  realms  on  high ; 
Great  is  the  theme,  though  weak  the  lay, 
For  my  heart  whispers  '  God  is  nigh.' 

The  Sun,  vicegerent  of  his  power, 
Shall  rend  the  veil  of  parting  night, 
Salute  the  spheres,  at  early  hour, 
And  pour  a  flood  of  life  and  light. 

Seven  circling  planets  I  behold, 
Their  different  orbits  all  describe  ; 
Copernicus  these  wonders  told, 
And  bade  the  laws  of  truth  revive. 

Mercury  and  Venus  first  appear, 
Nearest  the  dazzling  source  of  day  ; 
Three  months  compose  his  hasty  year, 
In  seven  she  treads  the  heav'nly  way. 

Next,  Earth  completes  her  yearly  course  ; 
The  Moon  as  satellite  attends ; 
Attraction  is  the  hidden  force. 
On  which  creation's  laws  depend. 

Then  Mars  is  seen  of  fiery  hue ; 
Jupiter's  orb  we  next  descry  ; 
His  atmospheric  belts  we  view, 
And  four  bright  moons  attract  the  eye. 

Mars  soomhis  revolution  makes, 

In  twice  twelve  months  the  sun  surrounds ; 

Jupiter,  greater  limit  takes. 

And  twelve  long  years  declare  his  Dounds. 

With  ring  of  light,  see  Saturn  slow, 
Pursue  his  path  in  endless  space  ; 
By  seven  pale  moons  his  course  we  know, 
And  thirty  years  that  round  shal  trace. 
11* 


liMf  THE    PLANETARY    StSTllSf 

The  Georgium  Sidus  next  appears, 
By  his  amazing  distance  known  ; 
The  lapse  of  more  than  eighty  years, 
In  his  account  makes  one  alone. 

Six  moons  are  his,  by  Herschel  shown,  \ 

Herschel  of  modern  times  the  boast ;  j 

Discovery  here  is  all  his  own,  j 
Another  planetary  host ! 

And  lo !  by  astronomic  scan,  .  j 

Three  stranger  planets  track  the  skies,  > 

Part  of  that  high  majestic  plan,  ; 
Whence  those  successive  worlds  arise. 

Next  Mars,  Piazzi's  orb  is  seen,  ] 

Four  years  six  months  complete  his  round  ;  | 

Science  shall  renovated  beam,  | 

And  gild  Palermo's  favoured  ground.  -' 

Daughters  of  telescopic  ray,  ■ 

Pallas  and  Juno,  smaller  spheres,  ^ 

Are  seen  near  Jove's  imperial  way,  '4 

Tracing  the  heavens  in  destined  years.  ■ 

Comets  and  fixed  stars  I  see, 

With  native  lustre  ever  shine ; 

How  great !  how  good  !  how  dreadful !  He, 

In  whom  life,  light,  and  truth  combine. 

Oh  !  may  I  better  know  his  will, 

And  more  implicitly  obey ; 

Be  God  my  friend,  my  father  still. 

From  finite — to  eternal  day.  Mangnall. 

Note.  The  foroojoing  rhymes  were  made,  probably,  before  Vesta 
was  discovered,  and  some  of  the  facts,  relating  to  the  other  new  pla- 
nets, not  so  well  ascertained  as  at  present.  Ceres  is  sometimes  called 
Piazzi,  after  the  discoverer. 


CHEMISTRY.  127 

LESSON  58.    .. 
Cliemistry. 

Chemistry  is  an  instructive,  interesting,  and  valuable 
science.  Within  the  last  sixty  years  its  empire  has  been 
wonderfully  extended.  There  is  scarcely  an  art  of  human 
life  which  it  is  not  fitted  to  subserve  ;  scarcely  a  department 
of  human  inquiry  or  labour,  either  for  health,  pleasure,  orna- 
ment, or  profit,  which  it  may  not  be  made  in  its  present  im- 
proved state,  eminently  to  promote.  To  the  husbandman 
this  science  furnishes  principles  and  agents  of  inestimable 
value.  It  teaches  him  the  food  of  plants,  the  choice  and 
use  of  manures,  and  the  best  means  of  promoting  the  vigour, 
growth,  productiveness,  and  preservation  of  the  various  vege- 
table tribes.  To  the  manufacturer  chemistry  has  lately  be- 
come equally  fruitful  of  instruction  and  assistance.  In  the 
arts  of  brewing,  tanning,  dyeing,  and  bleaching,  its  doc- 
trines are  important  guides.  In  making  soap,  glass,  pottery, 
and  all  metallic  wares,  its  principles  are  daily  applied,  and 
are  capable  of  a  still  more  useful  application,  as  they  be- 
come better  understood.  Indeed,  every  mechanic  art,  in 
the  different  processes  of  which  heat,  moisture,  solution,  mix- 
ture, or  fermentation  is  necessary,  must  ever  keep  pace  in 
improvement  with  this  branch  of  philosophy.  To  the  phy- 
siciar/  this  science  is  of  still  greater  value,  and  is  daily  grow- 
ing in  importance.  He  learns  from  it  to  compound  his  me- 
dicinesi,  to  disarm  poisons  of  their  force,  to  adjust  remedies 
to  diseases,  and  to  adopt  general  means  of  preserving  health. 

To  the  student  of  natural  history  chemistry  furnishes  in-^ 
struction  at  every  step  of  his  course.  To  the  public  econo* 
mist  it  ^resents  a  treasure  of  useful  information.  By  means  of 
this  science  alone  can  he  expect  to  attack  with  success  the  de- 
stroy in  ${  pestilence,  and  to  guard  against  other  evils  to  which 
the  state  of  the  elements  gives  rise.  And  to  the  successful 
prosecution  of  numberless  plans  of  the  philanthropist,  some 
acquamtance  with  the  subject  in  question  seems  indispensably 
necessary.  Finally,  to  the  domestic  economist  this  science 
abounds  with  pleasing  and  wholesome  lessons.  It  enables 
him  to  make  a  proper  choice  of  meats  and  drinks ;  it  di- 
rects h>m  to  those  measures  with  respect  to  food,  clothing,  a»d 


128  GENERAL    PRINCIPLES 

respiration,  which  have  the  best  tendency  to  promote  health, 
enjoyment,  and  cheapness  of  living ;  and  it  sets  him  on  his 
guard  against  many  unseen  evils,  to  which  those  who  are  ig- 
norant of  its  laws  are  continually  exposed.  In  a  word,  from 
a  speculative  science,  chemistry,  since  the  middle  of  the 
eighteenth  century,  has  become  eminently  and  extensively  a 
practical  one.  From  an  obscure,  humble,  and  uninteresting 
place  among  the  objects  of  study,  it  has  risen  to  a  high  and 
dignified  station  ;  and  instead  of  merely  gratifying  curio- 
sity, or  furnishing  amusement,  it  promises  a  degree  of  utility, 
of  which  no  one  can  calculate  the  consequences  or  see  the 
end. 

Questions. — 1.  What  dors  chemistry  do  for  the  husbandman? 
2.  For  the  manufacturer  ?  3.  For  the  mechanic  arts  ?  4.  For  the 
physician  ?  5.  For  the  student  of  natural  history  ?  C.  For  the  public 
economist?  7.  For  the  philanthropist?  8.  I  or  the  domestic  eco- 
nomist ? 


LESSON  59. 
General  Principles  of  Chemistry. 

The  object  of  chemistry  is  to  ascertain  the  ingredients  of 
which  bodies  are  composed, — to  examine  the  compounds 
formed  by  those  ingredients, — and  to  investigate  the  nature 
of  the  power  which  produces  these  combinations.  The 
science  therefore  naturally  divides  itself  into  three  parts :  a 
description  of  the  component  parts  of  bodies,  or  o^  elementa- 
ry or  simple  substances  as  they  are  called, — a  description 
of  the  compound  bodies  formed  by  the  union  of  simple  sub- 
stances,—^and  an  account  of  the  nature  of  the  power  which 
produces  these  combinations.  This  power  is  known  in 
chemistry  by  the  name  of  ajfmity,  or  chemical  attraction. 

By  simple  substances  is  not  meant  what  the  ancient  phi- 
losophers called  elements  of  bodies,  as  fire,  air,  earth,  and 
water,  nor  particles  of  matter  incapable  of  farther  diminu- 
tion or  division.  They  signify  merely  bodies  that  have  never 
been  decomposed,  or  formed  by  art.  The  simple  substances 
of  which  a  body  is  composed  are  called  the  constituent  parts 
#f  that  body  ;  and,  in  decomposing  it,  we  separate  its  co»- 


OF  CfiEMISTRY.  129 

Stituent  parts.  If,  on  the  contrary,  we  divide  a  body  by  cut- 
ting it  to  pieces,  or  even  by  grinding  it  to  the  finest  powder, 
each  of  these  small  particles  will  consist  of  a  portion  of  the 
several  constituent  parts  of  the  whole  body  :  these  are  called 
the  integrant  parts.  Compound  bodies  are  formed  by  the 
combination  of  two  or  more  simple  substances  with  each 
other. 

Attraction  is  that  unknown  force  which  causes  bodies  to 
approach  each  other.  Its  most  obvious  instances  are,  the 
gravitation  of  bodies  to  the  earth  ;  that  of  the  planets  towards 
each  other,  and  the  attractions  of  electricity  and  magnetism. 
But  that  attraction,  which  comes  under  the  more  immediate 
cognizance  of  chemists,  subsists  between  the  particles  of 
bodies  ;  and  when  it  operates  between  particles  of  the  same 
species,  it  is  called  the  attraction  of  cohesion,  or  the  attrac- 
tion of  aggregation  ;  but  when  between  the  particles  of  dif- 
ferent substances,  it  is  called  the  attraction  of  composition, 
chemical  attraction,  or  chemical  affinity.  The  attraction 
of  cohesion,  then,  is  the  power  which  unites  the  integrant 
particles  of  a  body  :  the  attraction  of  composition  that  which 
combines  the  constituent  particles.  When  particles  are 
united  by  the  attraction  of  cohesion,  the  result  of  such  a 
union  is  a  body  of  the  same  kind  as  the  particles  of  which  it 
is  formed ;  but  the  attraction  of  composition,  by  combining 
particles  of  a  dissimilar  nature,  produces  compound  bodies 
quite  different  from  any  of  their  constituents.  If,  for  in- 
stance, you  pour  upon  a  piece  of  copper,  placed  in  a  glass 
vessel,  some  of  the  liquid  called  nitric  acid  {aquafortis)  for 
which  it  has  a  strong  attraction,  every  particle  of  the  copper 
will  combine  with  a  particle  of  acid,  and  together  they  will 
form  a  new  body,  totally  different  from  either  the  copper  or 
the  nitric  acid.  If  you  wish  to  decompose  the  compound 
which  you  have  thus  formed,  present  to  it  a  piece  of  iron, 
for  which  the  acid  has  a  stronger  affinity  than  for  copper  ; 
and  the  acid  will  quit  the  copper  to  combine  with  the  iron, 
and  the  copper  will  be  what  the  chemists  call  precipitated, 
that  is  to  say,  it  will  be  thrown  down  in  its  separate  state, 
and  reappear  in  its  simple  form.  In  order  to  produce  this 
effect,  dip  the  blade  of  a  knife  into  the  fluid,  and  when  you 
take  it  out  you  will  observe  that,  instead  of  being  wetted 
with  a  bluish  liquid  like  that  contained  in  the  glass,  it  will 
be  covered  with  a  thin  coat  of  copper. 


130  CALORIC. 

The  simple  substances  were  said  very  lately  to  amount  to 
more  than  fifty  in  number,  but  since  the  truly  interesting 
and  very  important  discoveries  of  Sir  Humphrey  Davy,  and 
other  eminent  chemists,  it  is  scarcely  possible  to  say  what 
substances  are  not  compound  bodies.  But  it  will  be  most 
conducive  to  science  to  consider  all  those  substances  as 
simple,  which  no  mode  of  decompounding  has  yet  been  dis- 
covered. Simple  substances  naturally  divide  themselves 
into  two  classes.  Those  which  belong  to  the  first  class 
are  of  too  subtile  a  nature  to  be  confined  in  any  of  the  ves- 
sels which  we  possess.  They  do  not  sensibly  affect  the  most 
delicate  balance,  and  they  have  received  therefore  the  name 
of  itiiponderahle  bodies.  The  second  class  of  bodies  may  be 
confined  in  proper  vessels,  may  be  exhibited  in  a  separate 
state,  and  their  weight  and  other  properties  may  be  deter- 
mined. They  have  received  the  name  o^ pondei^ahle  bodies. 
The  imponderable  bodies  at  present  supposed  to  exist  are 
four,  light,  heat  or  caloric,  electricity,  and  magnetism.  The 
first  three  are  intimately  connected  with  chemistry,  but  mag- 
netism has  with  it  no  known  connexion. 

Questions. — 1.  What  is  the  object  of  chemistry?  2,  How  does 
the  science  divide  itself ?  3.  What  is  meant  by  simple  substances? 
4.  What  is  the  difference  between  decomposition  and  division  ?  5. 
How  are  compound  bodies  formed  ?  C.  What  is  attraction  and  its 
most  obvious  instances  ?  7.  Define  attraction  of  cohesion  and  attrac- 
tion of  composition.  8.  Wliat  are  the  results  of  each  of  these  kinds 
of  attraction  ?  9.  What  example  is  given  to  illustrate  chemical  affini- 
ty or  attraction  ?  10.  How  may  you  decompose  the  body  thus  formed  ? 
11.  Define  the  chemical  term  precipitate.  12.  What  is  said  of  the 
number  of  simple  substances?  13.  Into  what  two  classes  are  they  di- 
vided ?  14.  What  is  stated  as  the  ground  of  this  division  ?  15.  What 
are  the  four  imponderable  bodies  ? 


LESSON  60. 


Caloric. 


Chem'ically,  when  a  mere  mixture  of  two  or  more  substances  is 
made,  they  are  said  to  be  mechanically  united ;  but  when  each 
or  either  substance  forms  a  component  or  constituent  part  of  the 
product,  the  substances  have  formed  a  chemical  union. 

Heat  is  a  well  known  sensation  which  we  perceive  on 
touching  any  substance  whose  temperature  is  superior  to 


CALORIC.  131 

that  of  the  human  body.  Chemists  have  agreed  to  call  the 
matter  of  heat  caloric,  in  order  to  distinguish  it  from  the 
sensation  which  this  matter  produces.  Caloric  has  a  ten- 
dency to  diffuse  itself  equally  among  all  substances  that 
come  in  contact  with  it.  If  the  hand  be  put  upon  a  hot 
body,  part  of  the  caloric  leaves  the  hot  body,  and  enters  the 
hand  ;  this  produces  the  sensation  of  heat.  On  the  contra- 
ry if  the  hand  be  put  upon  a  cold  body,  part  of  the  caloric 
contained  in  the  hand  leaves  the  hand  to  unite  with  the  cold 
body  ;  this  produces  the  sensation  of  cold.  If  you  pour 
warm  water  into  one  basin,  cold  water  into  a  second,  and  a 
mixture  of  hot  and  cold  water  into  a  third  ;  then  put  the  one 
hand  into  the  cold  water  and  the  other  into  the  warm,  for 
two  minutes,  and  after  that  put  both  hands  into  the  luke- 
warm water,  to  the  one  hand  it  will  feel  cold  and  to  the  other 
hot.  Persons  ascending  from  the  burning  shores  of  Vera 
Cruz,  on  the  road  to  the  mountain  land  of  Mexico,  will  feel 
the  climate  become  colder,  and  will  put  on  their  great  coats, 
and  yet  they  will  meet  people  descending  complaining  of  the 
heat.  Cold  therefore  is  nothing  but  a  negative  quality,  sim- 
ply implying  the  absence  of  the  usual  quantity  of  caloric. 

Caloric  is  uniform  in  its  nature  ;  but  there  exist  in  all 
bodies  two  portions,  very  distinct  from  each  other.  The 
One  is  called  sensible  heat,  or  free  caloric  ;  the  other  latent 
heat,  or  combined  caloric.  Sensible  caloric  is  the  matter 
of  heat  disengaged  from  other  bodies,  or,  if  united,  not  chemi- 
cally united  with  them.  Latent  caloric  is  that  portion  of  the 
matter  of  heat  which  makes  no  sensible  addition  to  the  tem- 
perature of  the  bodies  in  which  it  exists.  Wrought  iron, 
though  quite  cold,  contains  a  large  portion  of  latent  caloric  ; 
and  if  it  be  briskly  hammered  for  some  time  on  an  anvil,  it 
will  become  red  hot  by  the  action  of  this  species  of  caloric, 
which  by  the  percussion  of  hammering  is  now  evolved  and 
forced  out  as  sensible  heat. 

Caloric  pervades  all  bodies ;  and  this  is  not  the  case  with 
any  other  substance  with  which  we  are  acquainted.  It  com- 
bines with  different  substances,  however,  in  very  different 
proportions  ;  and  for  this  reason,  one  body  is  said  to  have  a 
greater  capacity  for  caloric  than  another.  When  gaseous 
substances  become  liquid,  or  liquid  substances  solid,  by  this 
change  of  state  they  lose  in  a  great  measure  their  capacity 
for  caloric.     During  the  slaking  of  quick-lime,  the  caloric 


132  THERMOMETER. 

which  is  evolved  escapes  from  the  water  in  consequence  of 
its  changing  from  a  liquid  to  a  solid  form  by  its  union  with 
the  lime.  When  solid  bodies  become  liquid  or  gaseous, 
their  capacity  for  caloric  is  proportionately  increased.  If 
you  place  a  glass  of  water  in  a  mixture  of  equal  quantities 
of  snow  and  salt,  during  their  conversion  to  a  liquid,  the 
water  will  be  frozen  in  consequence  of  parting  with  its  ca- 
loric to  supply  the  increased  capacity  of  the  mixture. 

The  portion  of  caloric  necessary  to  raise  a  body  to  any 
given  temperature  is  called  its  specific  caloric.  The  instru- 
ment in  common  use  for  measuring  the  temperature  of  bodies 
is  called  a  Thermometer.  It  consists  of  a  glass  tube  con- 
taining a  portion  of  mercury,  with  a  graduated  scale  annex- 
ed to  it.  It  is  constructed  in  the  following  manner.  A 
small  bulb  is  blown  on  the  end  of  the  tube,  and  this  bulb 
and  a  part  of  the  tube  are  to  be  filled  with  mercury  which 
is  to  be  heated  till  it  boils.  This  ebullition  forces  out  the  air 
and  the  tube  is  hermetically  sealed  while  the  mercury  is 
boiling.  The  next  object  is  to  construct  the  scale.  It  is 
found  by  experiment,  that  melting  snow  or  freezing  water  is 
always  at  the  same  temperature.  If,  therefore,  a  thermo- 
meter be  immersed  in  the  one  or  the  other,  the  mercury  will 
always  stand  at  the  same  point.  It  has  been  observed,  too, 
that  water  boils  under  the  same  pressure  of  the  atmosphere 
at  the  same  temperature.  A  thermometer,  therefore,  im- 
mersed in  boiling  water,  will  uniformly  stand  at  the  same 
point.  Here,  then,  are  two  fixed  points,  from  which  a  scale 
may  be  constructed,  by  dividing  the  intermediate  space  into 
equal  parts,  and  carrying  the  same  divisions  as  far  above  and 
below  the  two  fixed  points  as  may  be  wanted.  When  a  ther- 
mometer is  brought  in  contact  with  any  substance,  the  mer- 
cury expands  or  contracts  till  it  acquires  the  same  tempera- 
ture ;  and  the  height  at  which  the  mercury  stands  in  the 
tube,  indicates  the  exact  temperature  of  the  substance  to 
which  it  has  been  applied.  It  will. not  show  the  absolute 
caloric  in  substances ;  for  it  cannot  measure  that  portion 
which  is  latent,  or  chemically  combined  with  any  body. 

Caloric  is  the  cause  of  fluidity  in  all  substances  capable  of 
becoming  fluid,  from  the  heaviest  metal  to  the  lightest  gas. 
It  insinuates  itself  among  their  particles  and  invariably  se- 
parates them  in  some  measure  from  each  other.  Thus  ice 
is  converted  into  water,  and  by  a  further  portion  of  caloriC; 


ATMOSPHERIC    AHl.  133 

into  steam.  We  have  reason  to  believe  that  every  solid  sub- 
stance on  the  face  of  the  earth  might  be  converted  to  a  fluid, 
or  even  to  a  vapour  or  gas,  were  it  submitted  to  the  action 
of  a  very  high  temperature  in  peculiar  circumstances.  Some 
bodies  give  out  their  superabundant  caloric  much  sooner 
than  others.  Iron  is  a  quicker  conductor  of  caloric  than 
glass,  and  glass  than  wood.  If  you  take  a  piece  of  iron  in 
one  hand,  and  a  piece  of  wood  in  the  other,  the  iron  feels 
cold,  the  wood  warmer,  though  the  thermometer  shows  that 
their  temperature  is  the  same.  Substances  usually  become 
more  dense  by  the  loss  of  caloric  ;  but  the  freezing  of  water 
is  a  striking  cxcejition  to  this  general  law  of  nature,  and  is  a 
memorable  instance  of  the  wisdom  and  provident  care  of  the 
Almighty,  when  he  established  the  laws  of  the  universe. 

QuKSTioNs. — 1.  What  is  heat?  2.  Why  is  the  matter  of  heat 
called  caloric  ?  3,  How  are  sensations  of  heat  and  cold  produced  ? 
4.  What  is  cold  ?  5.  What  is  sensible  caloric  ?  6.  Latent  caloric  ?  7. 
What  experiment  illustrates  this  ?  8.  Why  is  one  body  said  to  have 
a  greater  capacity  lor  caloric  tlian  another  ?  9.  How  do  bodies  lose 
their  capacity  for  caloric  ?  10.  Why  is  caloric  evolved  during  the 
slaking  of  quick-lime  ?  11.  When  is  a  capacity  for  caloric  increased  . 
12.  Describe  the  experiment.  13.  What  is  specific  caloric  ?  14.  Of 
what  use  is  a  thermometer  ?  15.  Of  what  does  it  consist  .'*  16.  How- 
is  it  constructed  ?  17.  How  is  caloric  the  cause  of  fluidity  .''  18.  What 
is  said  of  conductors  of  caloric  ?  19.  To  what  general  law  of  nature 
is  the  freezing  of  water  an  exception .-'  20.  What  are  the  difl'ereni 
kinds  of  thermometers  ?  (See  Appendix.)  21.  How  is  each  gra- 
duated ? 


LESSON  61. 

Atmospheric  Air. 

Gas.  When  solid  substances  are  rendered  permanently  aSriform 
by  heat,  the  air,  thus  produced,  is  called  a  gas.  All  the  gases 
are  compounds  of  solid  matter  and  caloric.  It  is  caloric  which 
separates  the  particles,  and  gives  to  the  whole  a  gaseous  form. 
The  permanency  of  the  gases  appears  to  be  owing  to  the 
strength  of  the  affinity  existing  between  caloric  and  their  bases, 
which  affinity  resists  every  reduction  of  temperature. 

The  atmosphere,  which  was  formerly  supposed  to  be  a 

simple  fluid,  is  composed  of  two  distinct  substances,  termed 

oxygen  gas  and  nitrogen  gas.     It  is  not  a  chemical  com,' 

pound,  but  a  mere  mixture  of  those  gaseous  substances  in 

12 


134  ATMOSPHERIC    AIR. 

the  proportion  of  21  of  the  former  and  79  of  the  latter.  It 
contains  also  about  one  part  in  every  thousand  of  carbonic 
acid  gas,  a  considerable  portion  of  water  in  a  state  of  elastic 
Fapour,  and  several  adventitious  substances. 

Oxygen  is  an  element  or  simple  substance  generally  dif- 
fused through  nature,  though  like  caloric  it  does  not  exist 
by  itself.  It  takes  its  name  from  two  Greek  words,  signify- 
ing that  which  produces  or  generates  acids,  because  one  of 
its  general  properties  is  to  form  acids  by  combining  with  dif- 
ferent substances,  which  are  called  the  bases  of  the  several 
acids.  Its  different  combinations  are  essential  to  animal 
life  and  combustion.  Acted  upon,  or  combined  with  caloric, 
it  becomes  oxygen  gas,  which  is  distinguished  from  all  other 
gaseous  matter  by  several  important  properties.  Inflamma- 
ble substances  burn  in  it  under  the  same  circumstances  as 
in  common  air,  but  with  infinitely  greater  vividness.  If  a 
taper,  the  flame  of  which  has  been  extinguished,  the  wick 
only  remaining  ignited,  be  plunged  into  a  bottle  filled  with 
it,  the  flame  will  instantly  be  re-kindled,  and  will  be  very 
brilliant,  and  accompanied  by  a  crackling  noise.  If  a  steel 
wire,  or  thin  file,  having  a  sharp  point,  armed  with  a  bit  of 
wood  in  a  state  of  inflammation,  be  introduced  into  a  jar 
filled  with  the  gas,  the  steel  will  take  fire,  and  its  combus- 
tion will  continue,  producing  a  most  brilliant  phenomenon. 
Oxygen  gas  is  a  little  heavier  than  atmospheric  air,  and  from 
its  being  absolutely  necessary  to  the  support  of  animal  life, 
it  has  been  called  vital  air. 

Nitrogen  is  a  substance  diffused  through  nature,  and  par- 
ticularly in  animal  bodies.  It  is  not  to  be  found  in  a  solid 
or  liquid  state  ;  but  combined  with  caloric,  it  forms  nitrogen, 
or  azotic  gas,  in  which  no  animal  can  breathe,  or  any  com- 
bustible burn.  It  is  uninflammable  and  somewhat  lighter 
than  atmospheric  air,  and  though,  by  itself,  it  is  so  noxious  to 
animals,  it  answers  an  important  end  when  mixed  with  oxy- 
gen gas  in  atmospheric  air.  Were  it  not  for  this  large  quan- 
tity of  nitrogen  in  the  atmosphere,  the  stimulating  power 
of  the  oxygen  would  cause  the  blood  to  flo'V  with  too  great 
rapidity  through  the  vessels;  the  consequence  of  which 
would  be,  that  the  life  of  man  would  not  be  protracted  to 
the  length  that  it  now  is.  The  vermilion  colour  of  the  blood 
is  owing  to  the  inhalation  of  oxygen  gas.  When  the  dark 
purple  blood  of  the  veins  arrives  at  the  lungs,  it  imbibes  the 


Water.  135 

vital  air  of  the  atmosphere,  which  changes  its  dark  colour 
to  a  brilliant  red,  rendering  it  the  spur  to  the  action  of  the 
heart  and  arteries,  the  source  of  animal  heat,  and  the  cause 
of  sensibility,  irritability,  and  motion.  With  regard  to  the 
nitrogen  that  is  combined  with  atmospheric  air,  the  great- 
est part  of  it  is  thrown  out  of  the  lungs  at  every  respira- 
tion, and  it  rises  above  the  head,  that  a  fresh  portion  of  air 
may  be  taken  in,  and  that  the  same  air  may  not  be  repeated- 
ly breathed.  The  leaves  of  trees  and  other  vegetables  give 
out  during  the  day  a  large  portion  of  oxygen  gas,  which, 
uniting  with  the  nitrogen  thrown  off  by  animal  respiration, 
keeps  up  the  equilibrium,  and  preserves  the  purity  of  the 
atmosphere.  In  the  dark,  plants  absorb  oxygen,  but  the 
proportion  is  small,  compared  to  wh*at  they  exhale  by  day. 

Questions. — 1.  Of  what  is  atmospheric  air  composed  .?  2.  What 
is  the  proportion  of  each,  and  what  other  substances  does  it  contain."* 
3.  What  is  oxygen  .-*  4.  Why  is  it  thus  named  .''  5.  How  does  it  be- 
come oxygen  gas  ?  6.  What  are  some  of  its  important  properties  ?  7. 
Why  has  it  been  called  vital  air.?  8.  What  is  nitrogen,  and  how  does 
it  form  nitrogen  or  azotic  gas  .''  9.  What  are  some  of  its  properties  ?  10. 
What  important  end  does  it  answer,  and  how  .''  11.  How  is  the  ver- 
milion colour  of  the  blood  produced  .-'  12.  What  becomes  of  the  ni- 
trogen that  is  thrown  out  of  the  lungs  ? — why  ?  13.  What  tends  to 
preserve  the  purity  of  the  atmosphere  .''  [Note.  Nitrogen  (pronounced 
Ni'tro-jen,)  is  called  azote  by  the  French  chemists  on  account  of  its 
being  so  destructive  of  life.  Oxygen,  (pronounced  ox'e-j6n,)  besides 
producing  most  of  the  acids,  is  necessary  also  to  the  production  of  the 
alkalies.] 


LESSON  62. 

Water. 

Cal'cine,  to  burn  in  the  fire  to  a  calx ; — calx  is  a  substance  easily 
reduced  to  powder.  EfFerves'cence,  an  intense  motion  whicn 
takes  place  in  certain  bodies,  occasioned  by  the  sudden  escape 
of  a  gaseous  substance. 

Water  was  formerly  considered  as  a  simple  substance, 
and  chemical  philosophers  were  for  a  long  time  unwilling 
to  allow  of  its  being  otherwise.  Its  compound  nature,  how- 
ever, has  been  fully  proved.  It  is  composed  of  eighty-eight 
parts  by  weight  of  oxygen,  and  twelve  of  hydrogen,  in  every 
hundred  parts  of  the  fluid.  It  is  found  in  four  states,  name- 
ly, solid  or  ice  ;  liquid  or  water ;  vapour  or  steam  ;  and  in  a 


136  WATER. 

State  of  composition  with  other  bodies.  Its  most  simple 
state  is  that  of  ice,  and  the  difference  between  liquid  water 
or  vapour  and  ice,  is  merely  that  water  contains  a  larger 
portion  of  caloric  than  ice,  and  that  vapour  is  combined  with 
a  still  greater  quantity  than  water.  However  long  we  boil  a 
fluid  in  an  open  vessel,  we  cannot  make  it  in  the  smallest  de- 
gree hotter  than  its  boiling  point,  for  the  vapour  absorbs  the 
caloric,  and  carries  it  off  as  fast  as  it  is  produced.  It  is 
owing  to  this,  that  all  evaporation  produces  cold.  An  ani- 
mal might  be  frozen  to  death  in  the  midst  of  summer,  by 
repeatedly  sprinkling  ether  upon  him,  for  its  evaporation 
would  shortly  carry  off  the  whole  of  his  vital  heat.  Water 
thrown  on  burning  bodies  acts  in  the  same  way  ;  it  becomes, 
in  an  instant,  converted  into  vapour,  and  by  thus  depriving 
them  of  a  large  portion  of  their  caloric,  the  fire,  as  we  term 
it,  is  extinguished.  Vapour  occupies  a  space  eight  hundred 
times  greater  than  it  does  when  in  the  form  of  water,  and 
the  expansive  force  of  steam  is  found  by  experiment  to  be 
much  greater  than  that  of  gunpowder.  There  is  reason  to 
believe  that,  in  time,  steam  may  be  applied  to  many  useful 
purposes  of  which  at  present  we  have  no  idea. 

Hydrogen  is  the  base  of  the  gas  which  was  formerly  called 
inflammable  air,  and  when  in  the  aeriform  state,  it  is  the  light- 
est of  all  ponderable  things.  If  you  put  a  quantity  of  filings 
of  zinc  into  a  vessel  which  has  a  glass  tube  adapted  to  it, 
and  then  pour  upon  them  sulphuric  acid  {oil  of  vitriol)  di- 
luted with  six  or  eight  times  its  quantity  of  water  ;  an  effer- 
vescence will  immediately  take  place,  the  oxygen  of  it  will 
become  united  to  the  n>etal,  and  the  hydrogen  gas  will  be 
disengaged,  and  may  be  conveyed  by  the  glass  tube  into  any 
proper  receiver.  While  it  is  rushing  through  the  tube,  it 
may  be  kindled  with  a  taper,  and  it  will  burn  with  a  long 
flame  like  a  candle.  In  the  burning  of  the  gas,  the  hydro- 
gen unites  with  the  oxygen  of  the  atmosphere,  and  the  result 
of  the  combination  is  flame  and  water.  It  has  been  sup- 
posed that  the  torrents  of  rain,  which  generally  accompany 
thunder  storms,  may  arise  from  a  sudden  combustion  of  hy- 
drogen and  oxygen  gases  by  means  of  lightning.  Hydrogen 
gas  is  only  one  fourteenth  of  the  weight  of  atmospheric  air, 
and  occupies  a  space  fifteen  hundred  times  greater  than  it 
possessed  in  its  aqueous  combination.  It  is  continually 
emanating  from  vegetable  and  animal  matters  during  their 


THE  EARTHS.  137 

decay,  and  is  evolved  from  various  mines,  volcanoes,  and 
other  natural  sources.  From  its  grejit  levity  it  has  general- 
ly been  used  to  fill  air-balloons. 

Water  is  said  to  be  in  a  state  of  composition  with  other 
bodies,  because  in  many  cases  it  becomes  one  of  their  com- 
ponent parts.  It  is  combined  in  a  state  of  solidity  in  marble, 
in  crystals,  in  spars,  in  gems,  and  in  many  alkaline,  earthy, 
and  metallic  salts,  both  natural  and  artificial,  to  all  of  which 
substances  it  imparts  hardness,  and  to  most  of  them  transpa- 
rency. Near  the  poles  water  is  eternally  solid ;  there  it  is 
similar  to  the  hardest  rocks,  and  may  be  formed  by  the  chisel 
of  the  statuary,  like  stone.  It  becomes  still  more  solid  in  the 
composition  called  mortar,  and  in  cements,  having  parted 
with  more  of  its  caloric  in  that  combination  than  it  does  in 
the  act  of  freezing.  If  you  take  some  ground  plaster  of 
Paris,  fresh  calcined,  and  mix  it  with  a  little  water,  the  affini- 
ty of  the  plaster  for  the  water  is  so  great,  that  in  a  few  minutes 
the  whole  will  be  converted  to  a  solid. 

Questions. — 1.  Of  what  is  water  compoGcd  ?  2.  In  what  four 
states  is  it  found  ?  3.  What  is  its  most  simple  state  ?  4.  What  is  the 
difference  between  liquid  water  or  vapour  and  ice  ?  5.  Why  cannot 
water  in  an  open  vessel  be  made  hotter  than  its  boiling  point  ?  6.  How 
may  an  animal  be  frozen  to  death  in  the  midst  of  summer  .''  7.  Why 
would  this  happen  ?  8.  Explain  the  extinguishing  of  fire  by  water. 
9.  What  space  does  vapour  occupy  .''  10.  What  is  said  of  the  expan- 
sive force  of  steam,  and  its  probable  application  .-'  11.  What  is  hydro- 
gen, and  how  may  hydrogen  gas  be  obtained  ?  12.  What  is  the  result 
of  kindling  hydrogen  gas  on  its  rushing  from  the  glass  tube .'  13. 
What  is  its  weight  and  what  space  does  it  occupy  ?  14.  In  what  sub- 
stances is  water  combined  in  a  state  of  solidity  ?  15.  Why  does  water 
become  solid  in  mortar  and  in  cements.''  [Note.  Hydrogen  (pron. 
Hi'dro-jen,)  takes  its  name  from  two  Greek  words  signifying  to  pro- 
duce water.] 


LESSON  63. 

The  Earths  and  Alkalies. 

The  earths  are  silex,  or  silica,  alumine,  glucine,  zircon,  yttria, 
magnesia,  barytes,  strontites,  and  lime  : — the  four  last  mention-^ 
ed  are  called  alkaline  earths. 

Stra'ta  (plural  of  stratum)  beds,  layers. 

Earths  are  such  incombustible  substances  as  arc  not 
4uctile,  are  mostly  insoluble  ir*  water  or  oil,  and  preserre 

12* 


138  THE  ALKALIE8. 

their  constitution  in  a  strong  heat.  Notwithstancling  tlic 
varied  appearance  of  the  earth  under  our  feet,  and  of  the 
mountainous  parts  of  the  world,  whose  diversified  strata  pre- 
sent to  our  view  substances  of  every  texture  and  of  every 
shade,  the  whole  is  composed  of  only  nine  primitive  earths ; 
and  as  three  of  these  occur  but  seldom,  the  variety  which  is 
produced  by  the  other  six  becomes  the  more  remarkable. 
One  of  the  most  valuable  earths  with  which  we  are  acquainted 
is  silex  or  pure  flint.  It  is  the  most  durable  article- in  the 
state  of  gravel  for  the  formation  of  roads  ;  it  is  a  necessary 
ingredient  in  earthenware,  porcelain,  and  cements  ;  it  is  the 
basis  of  glass,  and  of  all  vitreous  substances.  It  is  white, 
inodorous  and  insipid  in  its  pure  state,  and  the  various 
colours,  which  it  assumes  in  different  substances,  proceed 
from  the  different  ingredients  with  which  it  is  mixed..  Alu- 
mine  obtained  its  name  from  its  being  the  base  of  the  salt 
called  alum.  It  is  distributed  over  the  earth  in  the  form  of 
clay,  and  on  account  of  its  aptitude  for  moulding  into  dif- 
ferent forms,  and  its  property  of  hardening  in  the  fire,  is 
employed  for  various  useful  purposes.  In  making  earthen- 
ware, a  due  proportion  both  of  silex  and  alumine  are  neces- 
sary ;  for  if  alumine  alone  were  used,  the  ware  could  not  be 
sufficiently  burnt  without  slirinking  too  much,  and  even 
cracking  ;  and  a  great  excess  of  silex  would  lessen  the  te- 
nacity and  render  the  ware  brittle.  Lime  is  never  found 
pure  in  nature  ;  it  is  obtained  by  decomposing  calcareous 
matters  by  the  action  of  fire,  which  deprives  them  of  their 
acid.  In  its  pure  state  it  is  used  in  many  of  the  arts.  It  is 
employed  by  the  farmers  as  a  manure  ;  and  by  bleachers, 
tanners,  iron-masters  and  others,  in  their  several  manufacto- 
ries, and  in  medicine.  The  use  of  lime  in  agriculture  may 
be  attributed  to  its  property  of  hastening  the  dissolution  of 
all  animal  and  vegetable  matters,  and  of  imparting  to  the 
soil  a  power  of  retaining  a  quantity  of  moisture  necessary  for 
the  nourishment  and  vigorous  growth  of  the  plants.  Mag- 
nesia, besides  being  the  basis  of  several  salts,  is  of  great  use 
in  medicine  ;  and  is  employed  by  the  manufacturers  of  ena- 
mels and  porcelain. 

The  alkalies  are  distinguished  by  an  acrid  and  peculiar 
taste  ;  they  change  the  blue  juices  of  vegetables  to  a  green^ 
and  the  yellow  to  a  brown,  and  have  the  property  of  render- 
ing oils  nusciblq  with  water,     They  form  various  salts  b^ 


THE    ALKALIES.  139 

combination  witli  acids,  act  as  powerful  caustics  when 
applied  to  the  flesh  of  animals,  and  are  soluble  in  water 
Potash  and  soda  have  been  called  fixed  alkalies,  because 
they  will  endure  a  great  heat  without  being  volatilized  : 
and  yet  in  a  very  high  temperature  they  are  dissipated  in 
vapour.  They  were  formerly  considered  to  be  simple  sub- 
stances, but  they  are  now  found  to  be  compounds  of  metallic 
substances,  called  potassium  and  sodium,  with  oxygen.  They 
have  various  uses  in  surgery  and  medicine,  and  are  employ- 
ed in  large  quantities  by  the  glass-maker,  the  dyer,  the  soap- 
maker,  the  colour-maker,  and  by  many  other  manufacturers. 
Ammonia  is  so  extremely  volatile  as  to  exhale  at  all  known 
temperatures.  When  combined  with  carbonic  acid,  it  takes 
a  concrete  form,  and  a  beautiful  white  colour,  and  is  known 
in  commerce  by  the  name  of  volatile  salts.  With  muriatic 
acid  it  forms  what  is  termed  sal  ammoniac,  which  is  employ- 
ed in  many  of  our  manufactories,  particularly  by  dyers  to 
give  a  brightness  to  certain  colours.  In  tinning  metals  it  is 
of  use  to  cleanse  the  surfaces,  and  to  prevent  them  from 
oxydizing  by  the  heat  which  is  given  to  them  in  the  opera- 
tion. Ammonia  is  furnished  from  all  animal  substances  by 
decomposition.  The  horns  of  cattle,  especially  those  of  deer, 
yield  it  in  abundance,  and  it  is  from  this  circumstance  that 
a  solution  of  ammonia  in  water  has  been  called  hartshorn. 

Questions. — 1.  What  are  earths?  2.  What  the  names  of  the 
mne  earths  ?  3.  What  is  said  of  silex  ?  4.  Of  alumine  ?  5.  Of 
lime  ?  6.  Of  magnesia  ?  7.  How  are  alkahes  distinguished  ?  8. 
Why  are  potash  and  soda  called  fixed  alkalies  ?  9.  Of  what  are  they 
compounds  ?  10.  What  is  said  of  their  uses  ?  11.  From  what  is  am- 
monia furnished  .-"  12.  What  is  said  of  its  combinations  and  uses  ? 
[Note.  Besides  the  nine  earths,  above  enumerated,  we  have  now 
thorina,  which  is  a  rare  earthy  substance  lately  discovered.  A  new 
alkali,  called  lithia,  has  recently  been  discovered,  which,  like  potash 
and  soda,  is  found  to  be  a  metallic  oxyd  :  its  base  is  called  lithium, 
Three  new  vegetable  alkalies  have  also  been  discovered,  called  mor- 
phia, picrotoxino,  and  vauquelinc.  Clay,  as  it  exists  in  soils,  is  com- 
monly called  argillaceo'us  earth ;  and  lime  in  soils  is  called  calcar^- 
0iis  earth.] 


140  A«ID9. 


LESSON  64. 


Acids  and  Salts. 

Acids  which  contain  different  quantities  of  oxygen  are  distin-  i 
guished  by  their  termination.  The  name  of  that  which  con-  ■ 
tains  most  oxygen  ends  in  ic,  the  other  in  ous.  Thus  we  say  ^ 
sulphuric  acid,  and  sulphurous  acid.  All  salts  that  are  com-  ■ 
posed  of  acids  ending-  in  ic,  take  an  ending  in  ate  ;  as  sulphate  1 
of  lime,  a  compound  of  lime  with  sulphuric  acid.  All  salts  [ 
composed  of  acids  ending  in  ous,  take  an  ending  in  ite,  in-  i 
stead  of  ate ;  as  sulphite  of  lime.  When  there  is  an  excess  J 
of  acid,  the  preposition  super  is  added  ;  and  when  an  excess  of  | 
the  base,  then  sub  is  prefixed,  as  super-sulphate  of  potasji,  or  I 
sub-boratc  of  soda,  (borax.)  t 

The  name  acid,  in  the  language  of  chemists,  has  been  • 
given  to  all  substances,  whether  liquids  or  solids,  which  pro-  ; 
duce  that  sensation  on  the  tongue  which  we  call  sour.  Most  j 
of  the  acids  owe  their  origin  to  the  combination  of  certain  1 
substances  with  oxygen  ;  and  they  have  the  property  of  | 
changing  the  blue,  green,  and  purple  juices  of  vegetables  to  \ 
red,  and  of  combining  with  alkalies,  earths,  or  metallic  oxyds,  i 
so  as  to  compose  those  compounds  termed  salts.  The  acids  <| 
were  formerly  divided  into  three  classes,  mineral,  vegetable,  ; 
and  animal ;  but  the  more  useful  and  scientific  v/ay  of  di-  ; 
viding  them  is  into  two  classes  only.  The  undecomposable  ■] 
acids,  and  those  which  are  formed  with  two  principles,  are  ' 
comprised  in  the  first  class  ;.  while  those  acids  which  are  form-  ; 
ed  with  more  than  two  principles  compose  the  second  class.  | 

Sulphuric  acid  is  procured  by  burning  sulphur,  in  contact  * 
with  some  substance  containing  oxygen  ;  by  which  process  - 
the  sulphur  combines  with  the  oxygen,  and  becomes  acidi-  \ 
fied.  In  commerce  it  is  commonly  called  the  oil  of  vitriol. 
That  peculiar  acid  which  is  called  muriatic  is  usually  ob-  \ 
tained  from  muriate  of  soda,  which  is  the  chemical  name  | 
for  common  salt.  Carbonic  acid  is  a  combination  of  carbon  •] 
and  oxygen.  It  was  formerly  called  fixed  air,  en  account  j 
of  its  being  so  intimately  combined  in  chalk,  lime-stone,  and  f 
other  substances.  If  you  pour  some  diluted  sulphuric  acid  I 
over  pulverized  chalk  or  marble  contained  in  a  glass  ves-  | 
sel,  which  has  a  tube  connected  with  it,  an  effervescence  j 
will  take  place,  and  carbonic  acid  gas  will  escape  through  j 
the  tube,     This  gas  is  more  destructive  of  life  than  any  ; 


SALT&. 


141 


6tlier,  arid  it  extinguishes  flame  instantaneously.  Water  may 
be  made  by  pressure  to  absorb  three  times  its  bulk  of  this 
gas ;  by  which  it  acquires  an  acidulous  and  not  unpleasant 
taste.  Soda  water,  cider,  and  other  fermented  liquors  owe 
their  briskness  and  sparkling  to  the  presence  of  this  gas. 
Fatal  accidents  often  happen  from  the  burning  of  charcoal 
in  chambers,  for  wherever  charcoal  is  burned  this  gas  is 
always  formed.  It  so  often  occupies  the  bottoms  of  wells, 
that  workmen  ought  not  to  venture  into  such  places  without 
previously  letting  down  a  lighted  candle.  If  the  candle 
burns  they  may  enter  it  with  safety ;  if  not,  a  quantity  of 
quick-lime  should  be  let  down  in  buckets,  and  gradually 
sprinkled  with  water.  As  the  lime  slakes,  it  will  absorb  the 
gas,  and  the  workmen  may  afterwards  descend  in  safety. 

The  number  of  acids  that  are  well  known  amounts  to  more 
than  forty,  and  their  uses  are  so  many  and  important  that 
it  is  impossible  to  enumerate  them.  They  are  indispensable 
to  various  arts  and  manufactures;  they  are  employed  for 
culinary  purposes,  and  for  medicine  ;  they  act  an  important 
part  in  the  great  elaboratory  of  nature,  and  form  a  great 
proportion  of  many  of  the  mountainous  districts  of  the  globe 
in  their  various  combinations. 

The  precise  number  of  the  salts  is  not  known,  but  they 
probably  amount  to  more  than  two  thousand.  The  different 
salts  are  known  from  each  other  by  the  peculiar  figure  of 
their  crystals,  by  their  taste,  and  other  distinctive  or  specific 
characters.  The  separation  of  salts  from  the  water  in  which 
they  may  be  dissolved,  is  generally  effected  by  evaporation 
and  cooling.  When  a  certain  portion  of  the  water  of  solu- 
tion is  evaporated,  and  the  remainder  left  in  a  proper  tem- 
perature at  rest,  the  salts  will  shoot  into  crystals,  and  will  be 
found  dispersed  through  the  water  at  the  bottom  and  at  the 
sides  of  the  vessel,  and  sometimes  also  on  the  surface  of  the 
solution.  Their  crystallization  is  owing  to  the  abstraction 
of  the  heat  or  water  by  which  they  were  dissolved.  Crys- 
tallized salts  are  liable  to  changes  in  their  appearance  by 
exposure  to  atmospheric  air.  Some  have  so  great  an  af- 
finity for  water  that  they  absorb  it  with  avidity  from  the  at- 
mosphere, and  thus  becoming  moist  or  liquid,  they  are  said 
to  deliquesce.  Others,  having  less  affinity  for  water  than 
atmospheric  air  has,  lose  their  water  of  crystallization  by 
exposure,  and  readily  fall  into  powder.     Such  salts  are  said 


142  SALTS.  ^ 

i 

to  effloresce.  Salts  have  not  only  the:  property  of  dissolving' 
in  water,  but  by  exposure  to  great  heat  they  will  melt,  andl 
they  require  different  degrees  of  heat  to  put  them  in  a  statej 
of  fusion,  as  well  as  different  quantities  of  water  for  the;fi^ 
solution.  y 

Many  of  the  salts  are  found  native,  and  the  carbonate^^ 
sulphates,  and  muriates  are  the  most  frequent.  Chalk,' 
limestone,  and  marble,  are  all  included  in  the  term  carboH 
nate  of  lime.  Few  salts  are  more  copiously  disseminated^ 
than  the  sulphate  of  lime,  particularly  in  the  vicinity  of  Pai^ 
lis,  and  hence  its  name  Plaster  of  Paris.  Of  the  native  miik 
riates,  muriate  of  lime  occurs  with  rock-salt,  and  muriate  of] 
Imagnesia  is  found  in  abundance  in  sea-water ;  and  muriatol 
of  soda  not  only  exists  in  immense  quantities  in  the  ocean,^ 
but  vast  mountains  in  different  parts  of  the  world  are  en^ 
tirely  formed  of  this  salt.  Nitrate  of  potash,  known  by  thw 
more  familiar  name  of  nitre  or  salt-petre,  is  collected  in  vsm, 
rious  parts  of  the  globe.  Phosphate  of  lime,  which  is  thi^ 
basis  of  all  animal  bones,  exists  native  in  Hungary,  ani 
composes  several  entire  mountains  in  Spain.  Mountains  ofj 
salt  were  probably  formed  in  very  remote  ages,  and  bjl 
processes  of  which  we  can  form  no  idea.  It  may  be  sup^ 
posed,  however,  that  these  changes  have  been  slow  and^ 
gradual,  for  several  of  the  native  salts  exhibit  marks  of  regii-{ 
larity  and  beauty  in  their  crystallization,  which  cannot  b^ 
imitated  by  art. 

Q„UESTioNS. — 1.  To  what  substances  is  the  name  acid  given 
To  what  do  most  acids  owe  their  origin  ?  3.  How  do  they  form  salts  i 
4.  What  is  said  of  the  division  of  acids  ?  5.  How  is  sulphuric  aci 
procured  ?  6.  Muriatic  acid  ?  7.  What  is  carbonic  acid  ?  8.  Ho^ 
may  you  obtain  carbonic  acid  gas  ?  9.  What  are  some  of  the  propei 
ties  of  this  gas  ?  10.  Why  do  fatal  accidents  often  happen  from  t! ' 
burning  of  charcoal  ?  11.  How  may  it  be  destroyed  at  the  bo|tom  < 
wells  .-*  12.  What  is  said  of  the  number  and  uses  of  the  acids  ?  11 
How  are  the  different  salts  known  from  each  other  ?  14.  How  niaj 
salts  be  separated  from  their  water  of  solution  .''  15.  To  what  change! 
are  crystallized  salts  liable  on  exposure  to  atmospheric  air  ?  16.  Wha 
native  salts  are  mentioned  ?    17.  What  is  said  of  salt  mountains .' 


SIMPLE  COMBUSTIBLES.  143 


LESSON  65. 

Simple  Combustibles. 

E''fchers,  volatile  liquids  formed  by  the  distillation  of  some  of  the 
acids  with  alcohol.  APcohol,  rectified  spirit  of  wine.  It  is  al- 
ways the  same  from  whatever  kind  of  spirit  it  is  distilled  :  it  is 
the  purely  spirituous  part  of  all  liquors  that  have  undergone 
the  villous  fermentation. 

The  combinations  of  sulphur  are  denominated  sulphurets ;  of 
phosphorus,  p hasp hurets  ;  of  carbon,  carburets  ;  of  hydrogen, 
hydrurets  ;  the  sulphuret  of  iron,  for  instance,  is  the  union  of 
sulphur  with  iron. 

Most  of  the  simple  substances  are  combustible,  or  bear 
;ome  relation  to  combustion.  Light  and  caloric  are  evolved 
luring  combustion  ;  oxygen  is  the  principal  agent ;  and  hy- 
Irogen,  sulphur,  phosphorus,  carbon,  and  the  metals,  are  the 
ubjects,  or  the  true  instruments  of  this  process.  Hydrogen 
jas  may  be  combined  with  water,  sulphur,  pliosphorus,  or 
v^ith  carbon.  When  combined  with  phosphorus  it  forms 
(hosphuretted  hydrogen  gas,  which  takes  fire  whenever  it 
omes  m  contact  with  atmospheric  air.  The  elastic  sub- 
tance,  which  is  called  carburetted  hydrogen  gas,  is  carbon 
[issolved  in  hydrogen  ;  it  has  likewise  been  called  heavy 
nflammable  air.  It  is  this  gaseous  compound  which  has 
tccasioned  so  many  dreadful  accidents  to  miners,  who 
;all  it  the  fire-damp.  This  gas  is  procured  from  pit-coal  by 
[ry  distillation ;  and  from  its  inflammability  and  brilliant 
lame,  it  has  been  used  for  lighting  streets,  shops,  manufac- 
ories,  and  light-houses  on  the  sea-coast.  The  rate  at  which 
t  is  procured  is  trifling  compared  to  the  expense  of  oil  and 
allow. 

Phosphorus  is  a  solid  inflammable  substance,  which  burns 
It  a  very  low  temperature,  when  in  contact  with  oxygen  gas 
)r  atmospheric  air.  Many  amusing  experiments  may  be 
)erformed  with  it,  but  it  must  be  handled  with  extreme 
;aution.  If  you  fix  a  piece  of  solid  phosphorus  in  a  quill, 
nd  write  with  it  upon  paper,  the  writing,  in  a  dark  room, 
/ill  be  beautifully  luminous.  If  the  face  or  hands  be  rubbed 
I'ith  phosphuretted  ether,  they  will  appear,  in  a  dark  place, 
.s  though  on  fire,  without  danger  or  sensation  of  heat. 

Pure  carbon  is  known  only  in  the  diamond  ;  but  carbon 
a  the  state  of  charcoal  may  be  procured  by  heating  to  red- 


HP^^w 


144  CARBON.  I 

ness  a  piece  of  wood  closely  covered  with  sand  in  a  crucible,- 
so  as  to  preserve  it  while '  in  the  fire,  and  afterwards,  while] 
cooling,  from  the  action  of  the  atmosphere.  It  is  capable  ofj 
forming  various  combinations,  but  charcoal  is  that  witll 
which  we  are  most  familiar.  Carbon  is  not  only  a  compo*^ 
nent  part,  but  it  forms  nearly  the  whole  of  the  solid  basis  ofl 
all  vegetables,  from  the  most  delicate  flower  in  the  garden  to' 
the  huge  oak  of  the  forest.  It  not  only  constitutes  the  basis- 
of  the  woody  fibre,  but  is  a  component  part  of  sugar,  and  of  i 
all  kinds  of  wax,  oils,  gums,  and  resins,  and  of  these  again,^ 
how  great  is  the  variety  !  It  is  imagined  that  most  of  the, 
metals  may  be  combined  with  carbon  ;  but  at  present  wej 
know  only  of  its  combination  with  iron.  In  one  proportior* 
it  forms  cast  iron  ;  in  another,  steel  ;  and  in  a  third,  plum^ 
bago,  generally,  though  improperly,  called  black  lead.  Ther0t 
is  no  lead  in  its  composition.  Cast  iron  contains  about  onrf 
forty-fifth  of  its  weight  of  carbon, — steel  is  combined  witM 
about  one  part  of  carbon  in  two  hundred  of  iron, — and  plumJ 
bago,  or  carburet  of  iron,  has  been  found  to  consist  of  nearly^ 
nine  parts  of  carbon  to  one  of  iron.  Wrought  iron  differa 
from  cast  iron,  in  being  deprived  of  its  carbon  and  oxygei^ 
by  continued  heat  and  repeated  hammering,  which  render 
the  metal  malleable.  Steel  is  made  of  wrought  iron  by  va* 
rious  processes,  whereby  the  metal  resumes  a  small  portion^ 
of  the  carbon,  and  acquires  a  capacity  of  receiving  different 
degrees  of  hardness.  { 

The  metals  are  generally  procured  from  beneath  the  surl 
face  of  the  earth,  in  a  state  of  combination  either  with  othe| 
metals,  with  sulphur,  oxygen,  or  with  acids  ;  though  a  fev|r 
of  them  have  occasionally  been  found  in  a  state  of  purity^ 
Metals  are  the  great  agents  by  which  we   are  enabled  ti 
examine  the  recesses  of  nature  ;  and  their  uses  are  so  mul^j 
tiplied,  that  they  are  become  of  the  greatest   importance  ir 
every  occupation  of  life.     They  are  the  instruments  of  al 
our  improvements,  of  civilization  itself,  and  are  even  sub 
servient  to  the  progress  of  the  human  mind  towards  perfec 
lion.     They  differ  so  much  from  each  other,  that  natur  I 
seems  to  have  had  in  view  all  the  necessities  of  man,  in  oi 
der  that  she  might  suit  every  possible  purpose  his  ingenuit 
can  invent,  or  his  wants  require.     We  not  only  receive  th;  ' 
great  variety  from  the  hand  of  nature,  but  these  metals  ai 
rendered  infinitely  valuable  by  various  other  properties  th< 


OXYDS.  145 

possess ; — by  their  combustibility,  their  solubility  in  fluids, 
their  combinations  with  various  substances,  and  by  their 
union  with  each  other,  whereby  compounds  or  alloys  are 
formed,  extremely  useful  in  a  variety  of  arts,  manufactures, 
and  other  requisites  of  life.  By  combining  them  with  oxy- 
gen we  can  invest  them  with  neio  properties,  and  are  ena- 
bled to  employ  these  to  promote  the  progress  of  the  fine  arts, 
by  imitating  the  master-pieces  of  creation  in  the  production 
of  artificial  salts,  gems,  and  crystals,  of  every  colour  and  of 
every  shade. 

Questions. — 1.  What  are  the  simple  combustibles?  2.  What  is 
said  of  phosphorus  combined  with  hydrogen  gas  ?  3.  What  is  carbu- 
retted  hydrogen  gas  ?  4.  Wliat  do  miners  call  it  ?  5.  To  what  use 
may  it  be  applied  ?  6.  What  is  phosphorus  ?  7.  What  experiments 
may  be  performed  with  it  ?  8.  How  may  carbon  be  obtained  in  the 
state  of  charcoal  ?  9.  What  is  said  of  carbon  with  regard  to  vegeta- 
bles, sugar,  wax,  &c.  10.  What  is  said  of  its  combinations  with  iron  .> 
11.  In  what  slate  are  metals  generally  found  .'  12.  What  is  said  of 
the  utility  of  metals  .''  [Note.  Chlorine  (oxymuriatic  acid,)  boron 
and  fluorine  (the  bases  of  the  boric  and  fluoric  acids,)  and  a  substance 
of  recent  discovery,  called  iodine,  have  lately  been  added  to  the  list 
of  simple  substances,  (see  Appendix.)  Iodine  and  Chlorine  are  capa- 
ble of  forming  distinct  and  peculiar  acids  by  combination  with  Hydro- 
gen. They  form  various  other  compounds,  such  as  Iodides,  Chlori- 
des :  lodates,  Chlorates ;  lodurets,  Chlorurets,  &g. 


LESSON  QQ. 

Oxyds  and  Combustion. 

As  oxygen  can  combine  in  different  proportions  with  the  same  sim- 
ple substance,  the  products  have  been  designated  by  the  names 
oTprotoxyd,  dtutoxyd,  or  tritoxyd,  according  as  the  oxygen  en- 
tered into  it,  in  one,  two,  or  three  proportions ;  and  that  has 
been  called  peroxyd,  which  was  most  oxydated,  or  oxydized. 

Retort',  see  description  of  fig.  48,  in  Appendix. 

Any  metal  or  combustible  body  which  is  combined  with 
less  oxygen  than  is  sufficient  to  render  it  acid,  is  usually 
called  an  oxyd.  Whenever  a  substance  is  converted  into 
an  oxyd,  we  say  it  is  oxydized;  but  if  it  becomes  an  acid  by 
its  union  with  oxygen,  we  say  it  is  oxygenized.  The  mine- 
ral, the  animal,  and  the  vegetable  kingdoms,  all  furnish  mat- 
ters which  are  convertible  into  oxyds,  by  an  union  with 
oxygen.  Metallic  oxyds  are  formed  in  several  ways,  the  chief 
13 


146  COMBUSTION. 

of  which  are  by  the  access  of  atmospheric  air,  by  the  de- 
composition of  water,  and  by  the  decomposition  of  acids. 
Iron  may  be  mentioned  as  a  familiar  example  of  a  metal  be- 
coming oxydized  by  atmospheric  air.  It  is  well  known  that 
when  this  metal  is  exposed  to  air  and  moisture,  it  acquires 
rust,  or  in  other  words  its  surface  is  converted  to  an  oxyd, 
in  which  state  the  metal  will  be  found  to  have  acquired  an 
increase  of  weight.  Common  red  lead,  which  is  a  true  oxyd 
of  lead,  is  made  by  melting  that  metal  in  ovens  so  constructed 
as  to  have  a  free  access  to  atmospheric  air.  Gold,  silver, 
and  platina,  cannot  be  oxydized,  unless  in  a  very  high  tem- 
perature ;  and  with  respect  to  other  metals,  they  not  only 
differ  in  their  capacity  for  oxygen,  but  also  in  their  attrac- 
tion for  it ;  so  that  one  will  often  rob  the  other,  thus  reduc- 
ing the  first  oxyd  to  its  primitive  metallic  form.  If  you 
dissolve  some  quicksilver  in  nitric  acid,  and  after  dropping 
a  little  of  the  solution  upon  a  bright  piece  of  copper,  gently 
rub  it  with  a  piece  of  cloth,  the  mercury  will  precipitate  it- 
self upon  the  copper,  which  will  be  completely  silvered. 

With  regard  to  the  oxyds  of  nitrogen  ;  the  first  degree 
of  oxydizement  produces  nitrous  oxyd  ; — a  further  portion 
of  oxygen  nitric  oxyd,  and  they  are  both  in  a  state  of  gas. 
Nitrous  oxyd  gas  bears  the  nearest  resemblance  of  any  other 
to  atmospheric  air.  It  will  support  combustion  even  better 
than  common  air  ;  it  is  respirable  for  a  short  time,  and  it  is 
absorbed  by  water.  Persons  who  have  inhaled  this  gas  have 
felt  sensations  similar  to  those  produced  by  intoxication.  In 
some  people  it  produces  involuntary  muscular  motion  and  a 
propensity  to  leaping  and  running  ;  in  others,  involuntary  fits 
of  laughter ;  and  in  all,  high  spirits,  and  the  most  exquisite- 
ly pleasurable  sensations,  without  any  subsequent  feelings  of 
debility.  It  is  readily  procured  by  exposing  crystals  of  ni- 
trate of  ammonia,  in  a  retort,  to  the  heat  of  a  lamp,  by 
which  means,  the  ammoniacal  salt  is  decomposed,  and  this 
gas  is  evolved. 

Combustion  may  be  defined  to  be  a  process  by  which  cer- 
tain substances  decompose  oxygen  gas,  absorb  its  base,  and 
sutler  its  caloric  to  escape  in  the  state  of  sensible  heat.  The 
agency  of  oxygen  in  combustion  is  attributable  to  its  affinity 
for  combustible  bodies.  The  combustible  having  a  greater 
affinity  to  oxygen  than  oxygen  has  to  caloric,  the  oxygen 
gas  is  decomposed,  and  its  oxygen  combines  with  the  ignited 


COMBUSTION,  147 

body,  while  its  caloric,  becoming  free,  is  diffused  among  the 
surrounding   bodies.     Whenever   we   burn    a   combustible 
body,  a  continued  stream  of  atmospheric  air  flows  towards 
the  fire  place,  to  occupy  the  vacancy  left  by  the  air  that  has 
undergone  decomposition,  and  which,  in  its  turn,  becomes 
decomposed  also.     Hence  a  supply  of  caloric  is  furnished 
without  intermission,  till  the  whole  of  the  combustible  is 
saturated  with  oxygen.     As  the  combustible  burns,  light  is 
disengaged,  and  the  more  subtile  parts,  now  converted  by 
caloric  into  gas,  are  dissipated  in  that  state.     When  the 
combustion  is  over,  nothing  remains  but  the  earthy  parts 
of  the  combustible,  and  that  portion   which    is  converted, 
by  the  process,  into  an  oxyd,  or  an  acid.     The  smoke  which 
arises  from  a  common  fire  is  chiefly  water  in   the  state  of 
vapour,  with  a  mixture  of  carburetted  hydrogen  and  bitu- 
minous substances ;  part  of  the  water  comes  from  the  mois- 
ture of  the  fuel ;  the  other  part  is  formed  during  combus- 
tion, by  the  union  of  the  hydrogen  of  the  combustible  with 
the  oxygen  of  the  atmosphere.     The  agency  of  oxygen  in 
combustion  may  be  demonstrated  by  placing   a  lighted  can- 
dle under  a  glass  vessel  inverted  upon  a  plate  of  water.     It 
will  be  seen  that  the  candle  will  go  out  as  soon  as  it  has 
consumed  all  the  oxygen  contained  in  the  included  air,  and 
that  the  water  will  rise  up  in  the  vessel  to  fill  the  vacancy. 
In  the  decomposition  of  atmospheric  air  by  combustion,  it  is 
natural  to  ask  what  becomes  of  the  nitrogen  gas?    As  the 
oxygen  becomes  fixed  in  the  combustible  body,  its  caloric  is 
disengaged,  a  part  of  which  combines  with  the  nitrogen,  and 
carries  it  ofi"  in  the   form  of  rarefied  nitrogen  gas.     When 
bodies  are  burnt,  none  of  their  principles  are  destroyed.  We 
have  reason  to  think  that  every  particle  of  matter  is  inde- 
structible, and  that  the  process  of  combustion  merely  decom- 
poses the  body,  and   sets   its    several    component  parts    at 
liberty,  to  separate  from  each  other,  to  form   other  new  and 
varied  combinations.     It  was  said  of  old,  that  the  Creator 
weighed  the  dust,  and  measured  the  water,  when  he  made 
the  world.     The  first  quantity  is  here  still ;  and  though  man 
can  gather  and  scatter,  move,  mix,  and  unmix,   yet  he  can 
destroy  nothing  :  the  dissolution  of  one  thing  is  a  prepara- 
tion for  the  being,  and  the  bloom,  and  the  beauty  of  another. 
Something   gathers  up  all   the  fragments,  and  nothing  is 
lost. 


148  ELECTRICITY. 

Questions. — 1.  What  is  an  oxyd  ?  2.  What  are  the  principal 
ways  by  which  metallic  oxyds  are  formed  ?  3.  What  is  said  of  iron  as 
an  example  ?  4.  What  is  red  lead  and  how  ia  it  made  ?  5.  What  is 
said  01  me  di^erent  capacity  and  attraction  of  metals  for  oxygen  ?  6. 
What  experiment  is  given  for  illustration  ?  7.  What  is  said  of  the 
properties  of  nitrous  oxyd  gas  ?  8.  What  effects  does  it  produce  on 
being  inhaled  ?  0.  How  may  it  be  procured  ?  10.  How  may  combus- 
tion be  defined  ?  11.  How  is  the  process  of  combustion  explained.'' 
12.  What  remains  when  the  combustion  is  over  ^    13.  What  is  smoke  .' 

14.  How  may  the  agency  of  oxygen  in  combustion  be  demonstrated  ? 

15.  What  becomes  of  the  nitrogen  gas  .■*  16.  What  is  said  of  the  in- 
destructibility of  matter  .''  17.  What  is  a  retort  ^  (see  Appendix.) 
18.  How  may  chlorine  be  procured  ?  10.  What  is  said  of  the  attrac- 
tion of  chlorine  for  the  metals  ?  20.  How  is  combustion  defined  in  the 
Appendix,  and  oa  what  grounds  is  it  so  defined  ? 


LESSON  67. 

Electricity. 

Elec'tric.  The  first  electrical  phenomena  are  supposed  to  have 
been  observed  in  a  mineral  substance  called  ai.iber,  in  Greek 
elektron,  and  hence  the  fluid  or  power  has  been  denominated 
electric. 

The  surface  of  the  earth,  and  of  all  the  bodies  with  which 
we  are  acquainted,  is  supposed  to  contain  or  possess  a  power 
of  exciting  or  exhibiting  a  certain  quantity  of  an  exceed- 
ingly subtile  a-rent,  called  the  electric  fluid  or  power.  The 
quantity  usually  belonging  to  any  surface,  is  called  its  natu- 
ral share,  and  then  it  produces  no  sensible  effects  ;  but  when 
any  surface  becomes  possessed  of  more,  or  of  less,  than  its 
natural  quantity,  it  is  electrified,  and  it  then  exhibits  a  variety 
of  peculiar  and  surprising  phenomena  ascribed  to  the  power 
called  electric.  If  you  take  a  stick  of  sealing-wax  and  rub 
it  on  the  sleeve  of  your  coat,  it  will  have  the  power  of  at- 
tracting small  pieces  of  paper,  or  other  light  substances, 
when  held  near  them.  If- a  clean  and  dry  glass  tube  be 
briskly  rubbed  with  the  hand,  or  with  a  piece  of  flannel, 
and  then  presented  to  any  small  light  substances,  it  will  im- 
mediately attract  and  repel  them  alternately  for  a  consider- 
able time.  The  tube  is  then  said  to  be  excited.  If  an  ex- 
cited glass  tube,  in  a  dark  room,  be  brought  within  about 
half  an  inch  of  the  finger,  a  lucid  spark  will  be  seen  between 
the  finger  and  the  tube,  accompanied  with  a  snapping  noise, 
and  a  peculiar  sensation  of  the  finger.     Dry  flannel  clothes, 


ELECTllICITY.  149 

when  handled  in  the  dark,  frequently  exhibit  a  sparkling 
appearance,  attended  with  the  same  kind  of  noise  that  is 
heard  in  the  experiment  of  the  glass  tube. 

All  those  bodies  which  transmit  or  conduct  electricity 
from  one  surface  to  another,  are  called  conductors,  and  those 
surfaces  that  will  not  transmit  the  electric  power,  are  called 
electrics  or  non-conductors.     The  general  class  of  conduc- 
tors comprehends  metals,  ores,  and  fluids  in  their  natural 
state,  except  air  and  oils.     Vitrified  and  resinous  substances, 
amber,  sulphur,  wax,  silk,  cotton,  and  feathers,  are  electrics 
or  non-conductors.      Many  of  these,   such  as  glass,  resin,, 
and  air,  become  conductors  by  being  heated.     When  a  sur- 
face is  supposed  to  have  more  than  its  natural  quantity  of 
this  fluid,  it  is  said  to  be  positively  electrified  ;  and   when 
less  than  its  natural  share,  to  be  negatively  electrified.    When 
any  electrified  conductor  is  wholly  surrounded  by  non-con- 
ductors, so  that  the  electric  fluid  cannot  pass  from  it  along 
conductors  to  the  earth,  it  is  said  to  be  insulated.     The  hu- 
man body  is  a  good  conductor  of  electricity  ;   but  if  a  person 
stand  on  a  cake  of  resin,  or  on  a  stool  supported  by  glass 
legs,  the  electric  fluid  cannot  pass  from  him  to  the  earth, 
and   if  he  is  touched  by  another  person  standing  on  the 
ground,  the  same  sparkling  appearance  and  noise,  as  men- 
tioned  above,  will  be  exhibited.     Two  surfaces,  both  posi- 
tively, or  both  negatively  electrified,  repel  each  other  ;  and 
two  substances,  of  which  one  is  positively,  and  the  other 
negatively  electrified,  attract  each  other.     Opposite  electri- 
cities always  accompany  each  other,  for  if  any  surface  be- 
come positive,  the  surface  with  which  it  is  rubbed  becomes 
negative  ;  and  if  any  surface  be  rendered  positive,  the  near- 
est conducting  surface  will  become  negative.     When  one 
side  of  a  conductor  receives  the  electric  fluid,  its  whole  sur- 
face is  instantly  pervaded  ;  but  when  an    electric  or  non- 
conductor is  presented  to  an  electrified   body,  it  becomes 
electrified  on  a  small  spot  only.     If  to  one  side  of  a  pane  of 
glass,  you  communicate  positive  electricity,  the  opposite  side 
will  become  negatively  electrified,  and  the  plate  is  then  said 
to  be  charged.     These  electricities  cannot  come  together, 
unless  a  communication,  by  means  of  conductors,  is  made 
between  the  sides  of  the  glass;  and  if  their  union  be  made 
through  the  human  body,  it  produces  an  aifection  of  the 
nerves  called  an  electric  shock. 
13* 


150  EXPERIMENTS'. 

As  the  excitation  which  is  produced  by  rubbing  with  the 
hand  on  a  tube  or  plate  of  glass,  is  not  only  very  laborious, 
but  inadequate  to  the  production  of  any  material  quantity  of 
electric  fluid,  machines  have  been  constructed  of  various 
forms  for  this  purpose.  The  most  common  machine  con- 
sists of  a  glass  cylinder,  supported  by  two  glass  pillars,  and 
made  to  turn  by  a  crank  or  handle.  A  rubber,  or  cushion, 
of  leather,  spread  with  an  amalgam  of  mercury  and  zinc  or 
tin  is  fastened  to  a  spring,  which  proceeds  from  a  socket  ce- 
mented on  the  top  of  another  glass  pillar.  A  piece  of  black 
silk  is  fastened  to  the  cushion  and  extended  over  the  cylin- 
der, nearly  to  the  receiving  points,  to  prevent  the  fluid  from 
flying  off.  A  fourth  glass  pillar  supports  what  is  called  the 
prime  conductor,  which  is  made  of  hollov^  brass  or  tin  plate, 
and,  at  the  end  towards  the  cylinder,  has  a  collection  of 
pointed  wires,  and  at  the  other  end,  a  single  wire  terminated 
by  a  brass  ball.  A  small  chain  is  fastened  to  the  cushion, 
one  end  of  which  extends  to  the  floor  or  table.  It  serves 
to  conduct  the  fluid  in  passing  from  the  earth  to  supply  the 
machine.  When  the  cylinder  is  turned  swiftly,  the  electric 
fluid  passes  from  the  rubber  to  the  glass,  and  is  thence  con- 
veyed to  the  points  of  the  prime  conductor,  which  is  thus 
positively  electrified.  While  the  electric  fluid  is  collecting, 
it  produces  a  crackling  noise,  and  in  a  darkened  room  the 
flame  will  be  seen  spread  on  the  surface  of  the  cylinder.  If 
a  cylinder  be  made  of  resin,  the  electricity  is  the  reverse  of 
that  wliich  is  produced  by  tlie  smooth  glass  cylinder  and 
rubber  of  the  usual  machines ;  for  in  this  case  the  rubber 
partakes  of  the  positive,  and  the  cylinder,  and  prime  conduc- 
tor, is  electrified  with  the  negative.  This  difference  be- 
tween the  resin  and  glass  has  given  rise  to  v/hat  is  called  the 
double  current,  or  vitreous  and  resinous  electricity  ;  but  it  is 
generally  supposed  that  the  difference  arises  more  from  the 
eflfect  of  the  surfaces  that  act  on  each  other,  than  from  -any 
peculiar  qualities  in  the  different  bodies. 

Some  of  the  experiments  which  may  be  made  with  an 
electrical  machine  are  necessary  for  illustrating  the  laws  of 
electricity,  and  others  are  merely  entertaining.  If  the  inside 
of  a  glass  tumbler  be  electrified  by  presenting  it  to  a  pointed 
wire  extending  from  the  prime  conductor,  and  then  placed 
over  a  few  pith-balls  laid  upon  a  table,  the  balls  will  immedi- 
ately begin  to  lexip  up  along  the  sides  of  the  glass,  and  then 


EXPERIMENTS.  151 

b^ck  to  the  table ;  they  are  attracted  and  repelled  by  the 
electrified  inside  surface  of  the  glass,  the  electricity  of  which 
they  gradually  conduct  to  the  table.  If  a  person  having  long 
hair,  not  tied  up,  be  placed  upon  an  insulated  stand,  and,  by 
means  of  a  chain  be  connected  with  the  prime  conductor, 
when  the  machine  is  put  in  motion,  the  hairs  on  his  head,  by 
repelling  each  other,  will  stand  out  in  a  most  surprising  man- 
ner. A  piece  of  sponge,  filled  with  water,  and  hung  to  a 
conductor,  when  electrified  in  a  dark  room,  exhibits  a  most 
beautiful  appearance.  If  a  piece  of  sealing-wax  be  fastened 
to  a  wire,  and  the  wire  be  fixed  into  the  end  of  the  conduc- 
tor, and  the  wax  lighted,  the  moment  the  machine  is  worked, 
the  wax  will  fly  off  in  the  finest  threads  imaginable.  Take 
a  two  ounce  phial,  half  full  of  olive-oil,  pass  a  slender  wire 
through  the  cork,  and  let  the  end  of  it  be  so  bent  as  to  touch 
the  glass  just  below  the  surface  of  the  oil }  then  place  your 
thumb  opposite  the  point  of  the  wire  in  the  phial,  and  if,  in 
that  position,  you  take  a  spark  from  the  charged  conductor, 
the  spark,  in  order  to  reach  your  thumb,  will  actually  per- 
forate the  glass.  In  this  way  holes  may  be  made  all  round 
the  phial. 

Questions. — 1.  What  parts  of  bodies  contain  the  electric  fluid  ?- 
2.  When  is  a  body  said  to  be  electrified  ?  3.  What  experiment  may 
be  made  with  seahng-wax  ?  4.  When  is  a  glass  tube  said  to  be  ex- 
cited ?  5.  What  is  said  respecting  an  excited  tube  when  in  a  dark 
room.''  0.  What  are  conductors  of  electricity  .''  7.  Electrics,  or  non- 
conductors .''  8.  When  is  a  surface  positively,  and  when  negatively 
electrified.''  9.  When  is  a  conductor  said  to  be  insulated?  10.  What  is 
said  of  the  human  body  as  a  conductor  .'  11.  When  do  sJurfaces  repel, 
and  when  attract  each  other  ?  IS.  What  takes  place  when  a  conductor 
receives  the  electric  fluid  .'' — non-conductor .''  13.  When  is  a  plate 
of  glass  said  to  be  charged  .''  14,  What  is  an  electric  shock  ?  15. 
Describe  the  electrical  machine.  16.  What  are  some  of  the  experi- 
ments that  may  be  made  with  it  ?  (See  Electrical  Machine,  fig.  49.) 
[Note.  The  earliest  account  of  any  known  electrical  effect  is  by  the 
ancient  naturalists,  Thales  and  Theophrastus,  who  flourished,  the  fir.st 
600,  and  the  latter  300  years  before  the  present  era.] 


152  DR.  franklin's  discovery. 


LESSON  68. 


Electricity  {continued.) 
A  quoous,  watery.     Collapse',  to  fall  together. 

The  Ley  den  phial  is  a  glass  jar  coated  with  tin  foil  on  the 
inside  and  outside  within  about  three  inches  of  the  top  of 
its  cylindrical  part,  and  having  a  wire  with  a  brass  ball  at  its 
extremity.  This  wire  passes  through  a  cork  or  piece  of 
wood,  and  at  its  lower  extremity  is  a  small  chain,  or  wire, 
that  touches  the  inside  coating  in  several  places,  and  serves 
as  a  conductor  to  charge  the  jar  with  electric  fluid.  On 
bringing  the  ball  of  the  jar  near  the  prime  conductor,  after 
a  few  turns  of  the  machine,  tlie  jar  will  be  charged.  The 
discharging  rod  consists  of  two  brass  balls  attached  to  the 
ends  ©f  a  wire,  bent  in  the  form  of  a  semicircle,  and  fixed 
to  a  glass  handle.  When  one  of  the  balls  of  the  discharg- 
ing rod  is  applied  to  the  ball  of  the  jar,  and  the  other  to  the 
outside  coating,  a  communication  is  made  between  the  out- 
side and  inside  of  the  jar,  by  which  the  equilibrium  is  in- 
stantly restored  by  the  superabundant  electricity  passing 
from  one  side  to  the  other,  appearing  in  the  form  of  a  vivid 
flash,  and  accompanied  with  a  loud  report.  Any  number  of 
persons  may  receive  the  shock  together  by  laying  hold  of 
each  other's  hands,  the  person  at  one  end  touching  the  out- 
side of  the  jar,  and  the  person  at  tlie  other  end  bringing  his 
hand  near  the  ball  of  the  jar.  If  there  were  a  hundred  per- 
sons so  situated,  they  would  every  one  feci  the  shock  at  the 
same  instant.  The  electric  fluid  mny  be  thus  conveyed 
many  miles  in  a  moment  of  time.  When  great  force  is  re- 
quired from  the  electric  fluid,  a  number  of  jars  of  the  above 
description  are  connected  together  by  making  a  communi- 
cation between  all  their  outsides,  and  another  between  all 
their  insides.  In  this  manner  any  number  of  jars  may  be 
charged  with  the  same  facility  as  a  single  one,  and  from  the 
powerful  effect  of  the  electric  fluid,  when  it  is  thus  collect- 
ed, it  is  called  an  electrical  battery. 

The  Leyden  phial  received  its  name  from  the  birth-place 
of  the  discoverer,  who  was  a  native  of  Leyden  in  Holland. 
But  the  greatest  discovery  that  was  ever  made  in  electricity 
was  reserved  for  Dr.  Franklin,  in  America.    It  had  been 


THUNDER   AND    LIGHTNING.  153 

imagined  before  his  time  that  a  similarity  existed  between 
lightning  and  the  electric  fluid ;  but  Franklin  brought  this 
supposition  to  the  test,  and  proved  the  truth  of  it  by  the  sim- 
ple means  of  a  boy's  kite  covered  with  9,  silk  handkerchief 
instead  of  paper,  and  some  wire  fastened  in  the  upper  part, 
which  served  to  collect  and  conduct  the  fluid.  When  he 
had  raised  this  machine  into  the  atmosphere,  he  drew  elec- 
tric fluid  from  the  passing  clouds,  which  descended  through 
the  flaxen  string  of  the  kite  as  a  conductor,  and  was  after- 
wards drawn  from  an  iron  key  which  he  tied  to  the  line  at 
a  small  distance  from  his  hand.  This  important  experiment 
immediately  led  to  the  formation  of  conductors  to  secure 
buildings  from  the  effects  of  lightning. 

When  aqueous  vapour  is  condensed,  the  clouds  formed  are 
usually  more  or  less  electrical,  and  the  earth  belov^  them  be- 
ing brought  into  an  opposite  state,  a  discharge  takes  place 
when  the  clouds  approach  within  a  certain  distance,  consti- 
tuting lightning;  and  the  collapsing  of  the  air,  which  is  ra- 
refied in  the  electrical  circuit,  is  the  cause  of  the  thunder, 
which  is  moie  or  less  intense,  and  of  longer  or  shorter  du- 
ration, according  to  the  quantity  of  the  air  acted  upon,  and 
the  distance  of  the  place  where  the  report  is  heard  from  the 
point  of  the  discharge. 

In  gloomy  pomp,  whilst  awful  midnight  reigns, 
And  wide  o'er  earth  her  snournful  mantle  spreads, 
Whilst  deep-voiced  Thunders  threaten  guilty  heads, 

And  rushing  torrents  drown  the  frighted  plains. 

And  quick-glanced  Lightnings,  to  my  dazzled  sight, 
Betray  the  double  horrors  of  the  night : 

A  solemn  stillness  creeps  upon  my  soul. 
And  all  its  powers  in  deep  attention  die  ; 
My  heart  forgets  to  beat ;  my  steadfast  eye 

Catches  the  flying  gleam  ;  the  distant  roll, 
Advancing  gradual,  swells  upon  my  ear 
With  louder  peals,  more  dreadful  as  more  near. 

Awake,  my  soul,  from  thy  forgetful  trance  ! 

The  storm  calls  loud,  and  meditation  wakes ; 

How  at  the  sound  pale  Superstition  shakes, 
Whilst  all  her  train  of  frantic  fears  advance  ! 


154  FALLING    STARS, 

Children  of  darkness,  hence  !  fly  far  from  me  1 
And  dwell  with  guilt  and  infidelity  ! 

But  come,  with  look  composed,  and  sober  pace, 
Calm  Contemplation,  come  !  and  hither  lead 
Devotion,  that  on  earth  disdains  to  tread  ; 

Her  inward  flame  illumes  her  glowing  face, 
Her  upcast  eye,  and  spreading  wings,  prepare 
Her  flight  for  heaven  to  find  her  treasure  there. 

She  sees,  enraptured  through  the  thickest  gloom, 
Celestial  beauty  beam,  and  'midst  the  howl 
Of  warring  winds,  sweet  music  charms  her  soul ; 

She  sees  while  rifted  oaks  in  flames  consume, 
A  Father  God,  that  o'er  the  storm  presides. 
Threatens,  to  save, — and  loves,  when  most  he  chides. 

Chapone. 

Questions. — 1.  What  is  the  description  of  the  Leyden  phial  ?  2. 
How  is  it  charged  ? — how  discharged  ?  3.  What  experiment  may  be 
made  by  it  ?  4.  What  is  an  electrical  battery  ?  5.  What  great  dis- 
covery did  Dr.  Franklin  make, — and  by  what  means  ?  C.  To  what 
did  this  experiment  lead  .''  7.  What  is  lightning  .-' — thunder  ?  (See 
Leyden  phial,  fig.  50.) 


LESSON  09. 

Falling  Stars,  Water  Spouts,  and  Northern  Lights. 

Lam'bent,  playing  about,  gliding  over. 

Glo'ry,  a  circle  of  ra3's  which  surrounds  the  heads   of  saints  in 
pictures, — praise,  celebrity,  felicity  of  heave«. 

It  is  supposed  to  be  owing  to  the  electricity  of  the  atmo- 
sphere, that  we  observe  a  number  of  curious  and  interesting 
phenomena,  such  as  falling  stars,  water-spouts,  and  northern 
lights.  What  are  called  falling  stars  are  seen  chiefly  in  clear 
and  calm  weather :  it  is  then  that  the  electric  fluid  is  pro- 
bably not  very  strong,  and  passing  through  the  air  it  becomes 
visible  in  particular  parts  of  its  passage,  according  to  the  con- 
ducting substances  with  which  it  may  meet.  One  of  the 
most  striking  of  this  kind  is  recorded  by  Beccaria,  an  Ita- 
lian.— As  he  was  sitting  with  a  friend  in  the  open  air,  an 
hour  after  sun-set,  they  saw  a  falling,  or  as  it  is  sometimes 


NORTHERN   LIGHTS.  155 

called,  a  shooting  star,  directing  its  course  towards  them, 
growing  apparently  larger  and  larger,  till  it  disappeared  not 
far  from  them,  and,  disappearing,  it  left  their  faces,  hands, 
and  clothes,  with  the  earth,  and  neighbouring  objects,  sud- 
denly illuminated  with  a  diffused  and  lambent  light,  attend- 
ed with  no  noise  at  all.  He  concluded  this  to  be  the  effect 
of  electricity,  because  he  had  previously  raised  his  kite, 
and  found  the  air  very  much  charged  with  the  electric  matter  : 
sometimes  he  saw  it  advancing  to  his  kite  like  a  falling  star^ 
and  sometimes  he  saw  a  kind  of  glory  round  it,  which  fol- 
lowed it  as  it  changed  its  place. 

Water-spouts  are  often  seen  in  calm  weather  ;  and  the 
sea  seems  to  boil  and  send  up  smoke  under  them,  rising  in 
a  sort  of  hill  towards  the  spout.  A  rumbling  noise  is  often 
heard  at  the  time  of  their  appearance,  which  happens  gene- 
rally in  those  months  that  are  peculiarly  subject  to  thunder- 
storms, and  they  are  commonly  accompanied  or  followed  by 
lightning.  When  these  approach  a  ship,  the  sailors  present 
and  brandish  their  swords  to  disperse  them,  which  seems  to 
favour  the  conclusion  that  they  are  electrical.  The  analogy 
between  water-spouts  and  electricity  may  be  made  visible  by 
hanging  a  drop  of  water  to  a  wire,  communicating  with  the 
prime  conductor,  and  placing  a  vessel  of  water  under  it.  In 
these  circumstances,  the  drop  assumes  all  the  various  ap- 
pearances of  a  water-spout,  in  its  rise,  form,  and  mode  of 
disappearing.  It  is  inferred,  therefore,  that  the  immediate 
cause  of  this  extraordinary  phenomenon  is  the  attraction  of 
the  lower  part  of  the  cloud  for  the  surface  of  the  water. 

The  northern  light  {Aurora  BoreaUs)  is  an  extraordinary, 
meteor,  or  luminous  appearance,  showing  itself  in  the  night, 
in  the  northern  part  of  the  heavens  ;  and  most  frequently  in 
frosty  weather.  It  is  usually  of  a  reddish  colour  inclining  to 
yellow,  and  sends  out  frequent  coruscations  of  pale  light, 
which  seem  to  rise  from  the  horizon  in  the  form  of  a  pyra- 
mid with  undulating  motion,  and  shoot  with  great  velocity 
up  to  the  zenith.  This  kind  of  meteor^  which  is  more  un- 
common as  we  approach  towards  the  equator,  appears  with 
the  greatest  lustre  in  the  polar  regions,  and  during  the  long 
winter  is  almost  constant.  In  Sweden  and  Lapland,  the 
northern  lights  are  not  only  singularly  beautiful  in  their  ap- 
pearance, but  afford  travellers  by  their  almost  constant  ef- 
fulgence a  very  beautiful  light  during  the  whole  night.     In 


156  NORTHERN  LIGHTS.  ) 

Hudson's  bay,  they  diffuse  a  variegated  splendour,  which  in  ■ 

said  to  equal  that  of  the  full  moon.     In  the  north  eastern  j 

parts  of  Siberia,  they  have  been  described  as  beginning  with  I 
single  bright  pillars,  rising  in  the  north,  and  almost  at  the 

same  time  in  the  north-east,  which  gradually  increasing  com-  j 

prebend  a  large  space  of  the  heavens,  rush  about  from  place  ' 

to  place  with  incredible  velocity^  and  finally  almost  cover  the  i 

whole  sky.     The  northern  lights  are  supposed  to  be  electrical  i 

phenomena,  because  electricians  can  readily  imitate  the  ap-  i 
pearance  with  their  experiments.     Dr.  Franklin's  idea  is  that 

they  may  arise  from  a  discharge  of  electricity,  accumulated  ^ 

in  the  atmosphere  near  the  poles,  into  its  rarer  parts.  J 

On  the  Northern  Lights.  ■ 

BY  LOMONOSOV,  A    RUSSIAN  POET TRANSLATED  BY  J.  BOW-       j 

RING.  ^ 

Where  are  thy  secret  laws,  O  nature,  where  ?  .; 

Thy  north  lights  dazzle  in  the  wintry  zone  :  - 

How  dost  thou  light  from  ice  thy  torches  there  ?  \ 

There  has  thy  sun  some  sacred,  secret  throne  /  J 

See  in  yon  frozen  seas  what  glories  have  their  birth  j      J 
Thence  night  leads  forth  the  day  to  illumine  the  earth.    \ 

Come  then,  philosopher  !  whose  privileged  eye  ■ 

Reads  nature's  hidden  pages  and  decrees  ;  '\ 
Come  now,  and  tell  us  whence,  and  where,  and  why, 

Earth's  icy  regions  glow  with  lights  like  these,  j 

That  fill  our  souls  with  awe;  profound  inquirer,  say  ;  ^ 
For  thou  dost  count  the  stars  and  trace  the  planets'  way  ! 

What  fills  with  dazzling  beams  the  illumined  air?  \ 

What  wakes  the  flames  that  light  the  firmament  ?  ] 

The  lightning's  flash  ?  there  is  no  thunder  there — 
And  earth  and  heaven  with  fiery  sheets  are  blent  ; 
The  winter  night  now  gleams  with  brighter,  lovelier  ray 
Than  ever  yet  adorned  the  golden  summer's  day. 

Is  there  some  vast,  some  hidden  magazine, 

Where  the  gross  darkness  flames  supplies  1 

Some  phosphorus  fiibric,  which  the  mountains  screen, 

Whose  clouds  of  light  above  those  mountains  rise?  j 

Where  the  winds  rattle  loud  around  the  foaming  sea,       ; 

And  lift  the  waves  to  heaven  in  thundering  revelry  ?       ? 


GALVANISM 


157 


Thou  knowest  not !  'tis  doubt,  'tis  darkness  all ! 
E'en  here  on  earth  our  thoughts  benighted  stray, 
And  all  is  mystery  through  this  worldly  ball — 
Who  then  can  reach  or  read  yon  milky  way  ? 
Creation's  heights  and  depths  are  all  unknown,  untrod  ; 
Who  then  shall  say  how  vast,  how  great,  creation's  God? 

Questions. — 1.  Why  is  it  supposed  that  those  meteoric  appear- 
ances called  falling  stars  owe  their  origin  to  electricity  ?  2.  How  may 
the  analogy  between  electricity  and  the  water-spout  be  made  visible  ? 
3.  Describe  the  northern  light.  4.  What  is  Dr.  Franklin's  idea  of  it  ? 
[Note.  A  similar  light  calitd  aurora  australis  has  been  long  since  ob- 
served towards  the  south  pole.] 


LESSON  70. 

Galvanism. 
Mus'cle,  the  fleshy  fibrous  part  of  an  animal  body. 
Galvanism  is  another  mode  of  exciting  electricity.  In 
electricity  the  effects  are  chiefly  produced  by  mechanical 
action ;  but  the  effects  of  galvanism  are  produced  by  the 
chemical  action  of  bodies  upon  each  other.  This  branch 
of  philosophy  has  been  denominated  galvanism,  from  Galva- 
ni,  an  Italian  professor,  whose  experiments  led  to  its  dis- 
covery. In  1789,  he  was  by  accident  led  to  the  fact  of 
electricity  having  the  property  of  exciting  contractions  in 
the  muscles  of  animals.  After  having  observed  that  com- 
mon electricity,  even  that  of  lightning,  produced  vivid 
convulsions  in  the  limbs  of  recently  killed  animals,  he  ascer- 
tained that  metallic  substances,  by  mere  contact,  under  par- 
ticular circumstances,  excited  similar  commotions.  He 
found  it  to  be  essential  that  the  forces  of  metals  employed 
should  be  of  different  kinds.  He  applied  one  piece  of  metal 
to  tlje  nerve  of  the  part,  and  the  other  to  the  muscle,  and 
afterwards  connected  the  metals,  either  by  bringing  them 
together,  or  by  connecting  them  by  an  arch  of  a  metallic 
substance  ;  every  time  this  connexion  was  formed,  the  con- 
vulsions took  place.  The  greatest  muscular  contractions 
were  found  to  be  produced  by  zinc,  silver,  and  gold.  A  per- 
son may  be  made  sensible  of  this  kind  of  electric  action  by 
the  following  experiments.  If  he  place  a  piece  of  one  metal, 
as  a  half  crown  above,  and  a  piece  of  some  other  metal,  as 
14 


15S  VOLTAIC    BATTERY. 

zinc,  below  his  tongue,  by  bringing  the  outer  edge  of  these 
pieces  in  contact,  he  will  perceive  a  peculiar  taste,  and  in 
the  dark  will  see  a  flash  of  light.  If  he  put  a  slip  of  tin-foil 
upon  the  bulb  of  one  of  his  eyes,  and  a  piece  of  silver  in  his 
mouth,  by  causing  these  pieces  to  communicate,  in  a  dark 
place,  a  faint  flash  will  appear  before  his  eyes.  Galvani  sup- 
posed that  the  virtues  of  this  new  agent  resided  in  the  nerves 
of  the  animal,  but  Volta,  who  prosecuted  this  subject  with 
much  greater  success,  showed  that  the  phenomena  did  not 
depend  on  the  organs  of  the  animal,  but  upon  the  electrical 
agency  of  the  metals,  which  is  excited  by  the  moisture  of  the 
animal,  whose  organs  were  only  a  delicate  test  of  the  pre- 
sence of  electric  influence.  In  exciting  the  electricity  of 
the  pieces  of  silver  and  zinc,  the  saliva  of  the  mouth  answers 
the  same  purpose  as  the  moisture  of  the  animal. 

The  conductors  of  the  galvanic  fluid  are  divided  into  the 
perfect  and  imperfect.  The  perfect  conductors  consist  of 
metallic  substances  and  charcoal  :  the  imperfect  are  water 
and  oxydated  fluids,  as  the  acids  and  all  the  substances  that 
contain  these  fluids.  To  render  the  Galvanic,  or  more 
properly  the  Voltaic  power  sensible,  the  combination  must 
consist  of  three  conductors  of  the  different  classes.  When 
two  of  the  three  conductors  are  of  the  first  class,  the  combi- 
nation is  said  to  be  of  the  first  order ;  when  otherwise,  it  is 
said  to  be  of  the  second  order.  If  a  piece  of  zinc  be  laid 
upon  a  piece  of  copper,  and  upon  the  copper  a  piece  of  flan- 
nel, moistened  with  a  solution  of  salt  in  water  a«Vc/c  of  the 
first  class  is  formed  ;  and  then  if  three  other  pieces  be  laid 
on  these  in  the  same  order,  and  repeated  seveial  times,  the 
whole  will  form  a  pile  or  battery  of  the  first  order.  The  ef- 
fects may  be  increased  to  any  degree,  by  a  repetition  of  the 
same  simple  combination.  Tlie  following  is  a  cheap  and 
-easy  method  of  constructing  a  Voltaic  pile,  for  zinc  is  one  of 
the  cheapest  of  metals,  and  may  be  easily  melted,  like  lead. 
Let  a  person  cast  twenty  or  thirty  pieces  of  zinc,  of  the  size 
of  a  cent,  which  may  easily  be  done  in  moulds  made  of  clay. 
Let  him  then  take  as  many  cents,  and  as  many  pieces  of 
paper  or  woollen  cloth  cut  in  the  same  shape,  and  which  he 
is  to  dip  in  a  solution  of  salt  and  water.  In  building  the 
pile,  let  him  place  a  piece  of  zinc,  wet  paper,  the  supera- 
bundant water  being  pressed  out,  after  which  the  copper ; 
then  zinc,  paper,  copper,  and  so  on,  until  the  whole   be 


GALVANISM.  ISQ 

finished.  The  sides  of  the  pile  may  be  supported  with  rods 
of  glass,  or  varnished  wood,  fixed  in  the  board  on  which  it  is 
built.  Having  wet  both  hands,  touch  the  lower  part  of  the 
pile  with  one  hand,  and  the  upper  part  with  the  other, 
constant  little  shocks  of  electricity  will  be  felt  until  one 
hand  be  removed.  If  the  hand  be  brought  back  a  similar 
repetition  of  shocks  will  be  experienced.  Hold  a  silver 
spoon  in  one  hand,  and  touch  with  it  the  battery  in  the  lower 
part,  then  touch  the  upper  part  with  the  tongue  ;  the  bitter 
taste  is  extreme.  If  the  end  of  the  spoon  be  put  under  the 
eyebrow,  close  to  the  ball  of  the  eye,  a  sensation  will  be  felt 
like  the  burning  of  red-hot  iron,  but  which  ceases  the  instant 
the  spoon  is  removed.  The  plates  will  soon  become  oxy- 
dated,  and  require  cleaning  in  order  to  make  them  act. 

Questions. — 1.  What  is  galvanism  ?  2.  Give  an  account  of  the 
origin  of  this  branch  of  philosophy.  3.  How  may  a  person  be  n)acle 
sensible  of  this  kind  of  electric  action  ?  4.  What  was  the  discovery 
of  Volta  ?  5.  What  are  perfect  conductors  of  galvanic  fluid  .'' — im- 
perfect .''  6.  What  is  necessary  in  order  to  render  the  galvanic  or  vol- 
taic power  sensible  .''  7.  When  is  the  combination  said  to  be  of  the 
first  order  ? — second  order  ?  8.  How  may  a  pile  or  battery  of  the  first 
order  be  formed  .''  0.  What  is  a  cheap  and  easy  method  of  forming 
a  voltaic  pile  ?  10.  What  experiments  may  be  formed  with  such  a 
pile  ?  11.  Why  do  the  plates  require  cleaning  ?  (See  Voltaic  pile, 
fig.  47.) 


LESSON  71. 

Galvanism  (continued.) 

Lab'oratory,  a  room  fitted  up  with  apparatus  for  the  performance 

of  chemical  operations. 
Deflagrate,  to  burn  rapidly:  nitre  thrown  on  hot  coals  defla- 
grates.    When  accompanied  with  a  loud  noise  it  is  termed  d^t- 
o-na'tion. 
The  most  convenient  kind  of  galvanic  battery  consists  of 
a  trough  made  of  baked  wood,  three  inches  broad,  and  about 
as  deep ;  in  the  sides  of  the  trough  are  grooves  opposite  to 
each  other  ;  into  each  pair  of  grooves  is  fixed;  by  cement,  a 
plate  of  zinc  and  silver  soldered  together,  and  in  the  order 
of  silver  and  zinc ;  the  cement  must  be  filled  in  so  as  to  pre- 
vent any  communication  between  the  difierent  cells.     The 
cells  are  to  be  filled  with  water  and  nitrous  acid^  and  then 


160  GALVANISM. 

if  a  communication  be  made  between  the  first  and  last  cell, 
by  means  of  the  hands,  a  strong  shock  will  be  felt,  which 
will  be  repeated  as  often  as  the  contact  is  renewed.  Several 
persons,  by  joining  hands,  having  first  wetted  them  with  wa- 
ter, may  receive  the  shock. 

The  spark  from  a  powerful  galvanic  battery  acts  upon 
and  inflames  gun-powder,  charcoal,  cotton,  and  other  inflam- 
mable substances,  melts  all  metals  and  disperses  diamonds. 
Fill  the  battery,  described  above,  with  water  and  nitrous 
acid  in  the  proportion  of  nine  parts  of  water  and  one  of 
acid,  and  wipe  the  edges  of  the  plates  very  dry  ;  then  fasten 
two  wires  to  pieces  of  copper,  which  are  to  be  put  into  thej 
outer  cells,  and  in  order  to  hold  the  wires  they  must  be  sur- 
rounded to  a  sufficient  extent  with  little  glass  tubes.  If  the 
ends  of  the  wires  be  brought  together  on  a  plate  of  glass,  a 
spark  will  be  perceived  ;  and  if  gun-powder  be  laid  on  the 
glass  between  the  points  of  the  wires,  it  will  be  exploded. 

The  galvanic  battery  in  the  laboratory  of  the  Royal  Insti- 
tution at  London  consists  of  two  hundred  instruments,  con- 
nected together  in  regular  order,  each  composed  of  ten 
double  plates  arranged  in  cells  of  porcelain,  and  containing 
in  each  plate  thirty-two  square  inches ;  so  that  the  whole 
number  of  double  plates  is  two  thousand,  and  the  whole  sur- 
face one  hundred  and  twenty-eight  thousand  square  inches. 
This  battery,  when  the  cells  are  filled  with  sixty  parts  of 
water,  mixed  with  one  part  of  nitric  acid,  and  one  part  of 
sulphuric  acid,  affords  a  series  of  impressive  and  brilliant 
effects.  When  pieces  of  charcoal,  about  one  inch  long  and 
one-sixth  of  an  inch  in  diameter,  are  brought  near  each  other, 
a  bright  spark  is  produced,  and  more  than  half  the  volume 
of  charcoal  becomes  ignited  to  whiteness,  and  by  withdraw- 
ing the  points  from  each  other,  a  constant  discharge  takes 
place  through  the  heated  air,  in  a  space  equal  at  least  to  four 
inches,  producing  a  most  brilliant  ascending  arch  of  light, 
broad  and  conical  in  form  in  the  middle.  When  any  sub- 
stance is  introduced  into  this  arch,  it  instantly  becomes  ig- 
nited;  platina  melts  as  readily  in  it  as  wax  in  the  flame  of  a 
common  candle  ;  fragments  of  diamond,  and  points  of  char- 
coal, and  plumbago,  rapidly  disappear,  and  seem  to  evaporate 
in  it.  Such  are  the  decomposing  powers  of  electricity,  that 
not  even  insoluble  compounds  are  capable  of  resisting  their 
energy ;  for  glass,  when  moistened  and  placed  in  contact 


NEW    DEFLAGIIATOR.  161 

with  electrified  surfaces  from  the  voltaic  apparatus  is  slowly 
acted  upon,  and  the  alkaline,  earthy,  or  acid  matter  carried 
to  the  poles  in  the  common  order.  Not  even  the  most  solid 
aggregates,  nor  the  firmest  compounds,  are  capable  of  re- 
sisting this  mode  of  attack  ;  its  operation  is  slow,  but  the 
results  are  certain  ;  and  sooner  or  later,  by  means  of  it,  bodies 
are  resolved  into  simpler  forms  of  matter. 

The  effects  of  galvanism  on  metallic  bodies  are  greatly 
increased  by  using  plates  of  a  large  size ;  and  on  the  con- 
trary, the  shock  is  increased  by  multiplying  the  pairs  of 
plates.  The  shock  of  a  battery  containing  eighty  or  a  hun- 
dred pairs  of  plates,  of  three  or  four  inches  in  diameter,  is 
such  as  few  persons  would  be  willing  to  bear  more  than  once. 
At  the  same  time  such  a  battery  produces  but  feeble  effects 
when  passed  through  a  metallic  wire.  On  the  contrary,  if 
one  or  two  pairs  of  plates  containing  the  same  extent  of  sur- 
face be  used,  the  sensation  it  gives  is  hardly  to  be  felt,  while 
it  will  deflagrate  a  metallic  wire  of  considerable  size. 

Professor  Hare,  of  Philadelphia,  has  invented  a  new  me- 
thod of  extricating  the  Voltaic  influence,  by  so  connecting 
the  plates,  that,  in  effect,  only  two  great  surfaces  of  the  metals 
are  presented  to  each  other.  By  this  arrangement,  the  gal- 
vanic action  on  different  substances  has  presented  some  new 
phenomena,  and  the  common  theory  of  galvanism  must  un- 
dergo, it  is  thought,  a  radical  change.  The  calorific  princi- 
ple is  immensely  increased,  while  the  electric  shock  is  hardly 
to  be  perceived.  Charcoal  exposed  to  the  effects  of  this  new 
deflagrator  melts  into  globules  resembling  diamond,  and  the 
process  is  attended  with  a  most  intense  light.  If  mercury 
be  placed  in  the  hand,  and  the  back  side  of  the  hand  be  ap- 
plied to  the  negative  pole,  and  the  positive  pole  be  brought 
to  the  surface  of  the  mercury,  it  will  be  inflamed,  and  the 
hand  will  be  affected  with  no  disagreeable  sensation,  till  the 
mass  of  mercury  becomes  heated.  The  new  view,  which 
Professor  Hare  has  been  induced  to  offer,  is,  that  galvanism 
is  a  compound  of  electricity  and  caloric,  and  this  is  thought 
to  be  confirmed  by  the  action  of  his  machine. 

Questions. — 1.  What  is  the  most  convenient  kind  of  galvanic 
battery  ?  2.  What  is  the  effect  of  a  powerful  galvanic  battery  upon 
inflammable  substances  ?  3.  Describe  the  battery  at  the  Roj^al  Insti- 
tution in  London.  4.  What  effect  does  it  produce  upon  charcoal.? — 
other  substances  ?  5.  What  is  said  of  the  effects  of  galvanism  by 
14* 


1^  MAGNETISM. 

using  plates  of  a  largo  size  ? — by  multiplying  the  pairs  of  plaice  ?  G, 
What  is  the  invention  of  Prof  Hare  ?  7.  What  experiments  may  be 
performed  with  it  ?  8.  What  new  view  of  the  subject  has  Prof.  Hare 
offered  ?  (See  the  galvanic  or  voltaic  battery  described  at  the  begin- 
ning of  this  lesson,  fig.  46.)  [Note.  Prof  Hare  has  named  his  new 
apparatus  Calorimotor,  or  heat  mover.] 


LESSON  72. 

Magnetism. 

Polar'ity,  that  property  of  a  mngnet,  by  which,  if  left  at  liberty, 
it  will  point  towards  the  poles  of  the  earth,  or  nearly  so  :  the 
same  end  always  points  to  the  same  pole. 

Although  the  phenomena  of  the  magnet  have,  for  many 
ages,  engaged  the  attention  of  natural  philosophers,  not  only 
by  their  singularity  and  importance,  but  also  by  the  obscu- 
rity in  which  they  are  involved  ;  yet  very  few  additions  have 
been  made  to  the  discoveries  of  the  first  inquiries  into  the 
subject.  No  hypothesis  has  hitherto  been  framed,  that  will 
account  in  an  easy  and  satisfactory  manner,  for  all  the  va- 
rious properties  of  the  magnet,  nor  have  the  links  of  the 
chain,  which  connect  it  with  the  other  phenomena  of  the 
universe,  ever  been  pointed  out.  It  is  certain,  indeed,  that 
both  natural  and  artificial  electricity  will  give  polarity  to 
needles,  and  even  reverse  a  given  polarity  ;  and  hence  it 
may  be  inferred  that  there  is  a  considerable  affinity  between 
the  electric  and  magnetic  powers,  but  in  what  manner  elec- 
tricity acts  in  producing  magnetism,  is  still  utterly  unknown. 

The  ancients  were  acquainted  with  the  attractive  and  re- 
pulsive powers  of  the  magnet ;  but  it  does  not  appear  that 
they  knew  of  its  tendency  to  tiie  pole :  this  very  fortunate 
discovery  was  made  about  the  beginning  of  the  fourteenth 
century,  when  the  spirit  of  exploring  distant  regions  was 
gradually  forming  in  Europe.  The  use  which  might  be 
made  of  it  in  directing  navigation  was  immediately  perceived, 
and  that  most  valuable,  but  now  familiar  instrument,  the 
mariner's  compass,  invented.  When  navigators  found  that 
they  could,  at  all  seasons,  and  in  every  place,  discover  the 
north  and  south  with  the  greatest  ease  and  accuracy,  it  be- 
came^no  longer  necessary  to  depend,  like  the  voyagers  of 
former  ages,  merely  on  the  light  of  the  stars,  and  the  obser 


MAGNETISM.  163 

vation  of  the  sea-coast.  They  gradually  abandoned  their 
ancient  timid  and  lingering  course  along  the  shore  and  ven- 
tured boldly  into  the  ocean.  Relying  on  this  new  guide, 
they  could  steer  in  the  darkest  night,  and  under  the  most 
cloudy  sky,  with  a  security  and  precision  till  then  unknown. 
The  compass  may  be  said  to  have  opened  to  man  the  do- 
minion of  the  sea,  and  to  have  put  him  in  full  possession  of 
the  earth,  by  enabling  him  to  visit  every  part  of  it. 

Nearly  half  a  century  elapsed,  from  the  time  of  this  dis- 
covery, l3efore  navigators  ventured  into  any  seas  which  they 
had  not  been  accustomed  to  frequent.  But  in  the  course  of 
the  fifteenth  century,  discoveries  were  made  far  beyond  the 
conception  of  all  former  ages.  In  the  first  voyage  of  Co- 
lumbus, the  Spaniards  were  struck  with  an  appearance,  not 
less  astonishing  than  new.  They  observed  that  the  mag- 
netic needle,  in  their  compasses,  did  not  point  exactly  to 
the  polar  star,  but  varied  toward  the  west ;  and,  as  they 
proceeded,  this  variation  increased.  This  appearance, 
which  filled  the  companions  of  Columbus  with  terror,  and 
which  still  remains  one  of  the  mysteries  of  nature,  is  that 
deviation  from  the  meridian  which  is  called  the  variation  of 
the  needle.  It  is  different  in  different  parts  of  the  world  ; 
being  west  at  some  places,  east  at  others,  and  in  parts  where 
the  variation  is  of  the  same  name,  its  quantity  is  very  dif- 
ferent. It  is  the  same  to  all  needles  in  the  same  place  ;  and 
for  a  long  time,  it  was  thought  to  be  invariably  the  same,  at 
the  same  place,  in  all  ages ;  but  it  was  discovered,  about  tMc 
year  1625,  that  it  was  different  at  different  times,  in  the 
same  place.  From  subsequent  observations,  it  appears,  that 
this  deviation  was  not  a  constant  quantity,  but  that  it  gra- 
dually diminished  ;  and  at  last,  about  the  year  1660,  it  was 
found  that  the  needle  at  London  pointed  exactly  north.  At 
present  the  declination  at  London  is  about  twenty-four  de- 
grees west.  For  some  years,  it  has  been  nearly  stationary ; 
but  it  is  understood  now  to  be  returning  in  an  easterly  di- 
rection. Knowing  the  variation,  or  declination  of  the  mag- 
netic needle,  that  is,  the  angle  which  the  magnetic  meridian 
makes  with  the  meridian  of  the  place,  mariners  are  able  to 
sail  by  the  compass  with  as  much  accuracy  as  if  it  pointed 
exactly  north. 

The  inclination,  or  dipping  of  the  magnetic  needle,  ex- 
presses the  property  which  the  magnet  possesses  of  inclining 


164  MAGNETICAL  EXPERIMENTS, 

one  of  its  poles  towards  the  horizon,  and  of  elevating  the 
other  pole  above  it.  This  property  was  discovered  in  the 
year  1576,  It  is  found  to  be  always  the  same  at  the  same 
place,  but  different  in  different  places. 

Questions. — 1.  When  was  the  polarity  of  the  magnet  discovered? 
2.  What  use  was  made  of  this  property  of  the  magnet  ?  3.  When  and 
by  whom  was  the  deviation  of  the  needle  from  the  meridian  discovered  ? 
4.  What  is  said  of  this  variation  with  respect  to  the  same  place  ? — to 
different  places  ?  5.  What  is  said  of  the  declination  of  the  needle  at 
London?  6.  What  is  the  inclination  or  dipping  of  the  magnetic 
needle  ? 


LESSON  73. 

Magnetical  ExpenHmcnts. 

The  natural  magnet,  or  loadstone,  is  found  in  the  earth, 
generally  in  iron  mines,  in  a  hard  and  brittle  state,  and  for 
the  most  part,  more  vigorous  in  proportion  to  the  degree  of 
hardness.  Artificial  magnets,  which  must  be  made  of  hard 
or  highly  tempered  steel,  are  now  generally  used  in  prefer- 
ence to  the  natural  magnet ;  not  only,  as  they  may  be  pro- 
cured with  greater  ease,  but  because  they  are  far  superior  to 
the  natural  magnet  in  strength,  communicate  the  magnetic 
virtue  more  powerfully,  and  may  be  varied  in  their  form 
more  easily.  In  making  artificial  magnets,  care  should  be 
taken  to  apply  the  north  pole  of  the  natural  magnet  or  mag- 
nets to  that  extremity  of  the  steel  which  is  required  to  be 
made  the  south  pole,  and  to  apply  the  south  pole  of  the  mag- 
net to  the  opposite  extremity  of  the  piece  of  steel.  Very 
powerful  magnets  may  be  formed  by  first  constructing  several 
weak  magnets,  and  then  joining  them  together  to  form  a 
compound  one. 

The  north  or  south  poles  of  two  magnets  repel  each  other  ; 
but  the  north  pole  of  one  utfracfs  the  south  pole  of  another. 
The  attraction  between  the  magnet  and  iron  is  mutual,  for 
the  iron  attracts  the  magnet  as  much  as  the  magnet  attracts 
the  iron  ;  since  if  they  be  placed  on  pieces  of  wood,  so  as  to 
float  upon  the  surface  of  the  water,  it  will  be  found  that  the 
iron  advances  towards  the  magnet  as  well  as  the  magnet  to- 
wards the  iron,  or,  if  the  iron  be  kept  steady,  then  the  mag- 
net will  move  towards  it. 


MAGNETIC  EXPERIMENTS.  165 

Magnetic  attraction  will  not  be  destroyed  by  interposing 
obstacles  between  the  magnet  and  iron.  If  you  lay  a  small 
needle  on  a  piece  of  paper,  and  put  a  magnet  under  the  pa- 
per, the  needle  may  be  moved  backwards  and  forwards  ;  and 
with  a  piece  of  glass  or  board  the  effect  will  be  the  same. 
This  property  of  the  magnet  has  afforded  the  means  of  seve- 
ral amusing  deceptions.  A  small  figure  of  a  man  has  been 
made  to  spell  a  person's  name.  The  hand,  in  which  was  a 
piece  of  iron,  rested  on  a  board,  under  which  a  person,  con- 
cealed from  view,  with  a  powerful  magnet,  contrived  to  carry 
it  from  letter  to  letter,  until  the  word  was  made  up.  If  the 
figure  of  a  fish,  with  a  small  magnet  concealed  in  its  mouth, 
be  thrown  into  the  water,  and  a  baited  hook  be  suspended 
near  it,  the  magnet  and  iron  by  mutual  attraction  will  bring 
the  fish  to  the  bait. 

If  you  lay  a  sheet  of  paper,  covered  with  iron  filings  upon 
a  table,  with  a  small  magnet  among  them,  and  then  shake 
the  table  a  little,  at  the  two  ends  or  tl)e  poles,  the  particles 
of  iron  will  form  themselves  into  lines,  a  little  sideways, 
which  bend,  and  then  form  complete  arches,  reaching  from 
some  point  in  the  northern  half  of  the  magnet  to  some  other 
point  in  the  southern  half.  If  you  shake  some  iron-filings 
through  a  gauze  sieve  upon  a  paper  that  covers  a  bar  magnet, 
they  will  be  arranged  in  beautiful  curves. 

Soft  iron  is  attracted  by  the  magnet  more  forcibly  than 
steel,  but  it  is  not  capable  of  preserving  the  magnetic  pro- 
perty so  long.  The  gradual  addition  of  weight  to  a  magnet 
kept  in  its  proper  situation,  increases  the  magnetic  power, 
but  heat  weakens  it,  and  great  heat  destroys  it.  Bars  of 
iron  that  have  stood  long  in  a  perpendicular  situation,  are 
generally  found  to  be  magnetical ;  this  circumstance,  toge- 
ther with  the  phenomena  of  the  compass  and  the  dipping 
needle,  leaves  no  room  to  doubt  but  that  the  cause  exists 
within  the  earth. 

Questions. — 1.  Where  is  the  natural  magnet  found?  2.  Why 
are  artificial  magnets  used  in  preference  to  natural  ?  3.  How  may 
very  powerful  magnets  be  formed  ?  4.  How  do  the  poles  of  a  mag- 
net attract  and  repel  each  other  ?  5.  How  does  it  appear  that  the  at- 
traction between  the  magnet  and  iron  is  mutual  ?  G.  How  does  it 
appear  that  magnetic  attraction  will  not  be  destroyed  by  the  interpo- 
sition of  bodies  ?  7.  What  amusing  deceptions  has  the  attractive  pro- 
perty of  the  magnet  afforded  ?  8.  How  may  the  magnetic  power  be 
weakened  or  destroyed  ?  9,  From  what  is  it  concluded  that  the  cause 
of  magnetism  exists  in  the  earth  .' 


1^  AEROSTATION. 


LESSON  74. 


Aerostation. 

Wick'er,  made  of  small  sticks.     A'eronaut,  one  who  sails  through.    ! 

the  air.  i 

Meteorolog'ical,  relating  to  the  phenomena  of  the  atmosphere,  \ 

such  as  the  alterations  of  its  weight  and  temperature,  changes    \ 

produced  by  evaporation  and  rain,  its  excessive  agitations,  its     \ 

electricity,  &c.  ' 

Aerostation,  in  the  modern  application  of  the  term,  sig-  i 
nifies  the  art  of  navigating  through  the  air,  both  in  its  prin-  I 
ciples  and  practice.     Hence  also  the  machines  which  are    ; 
employed  for  this  purpose,  are  called  aerostats,  or  aerostatic    \ 
machines  ;  and  on  account  of  their  round  figure,  air-balloon^. 
Air-balloons  are  of  two  kinds,  those  filled  with  rarefied  air,    j 
and  those  filled  with  hydrogen  gas.     The  best  forms  for  bal- 
loons are  globular  or  oval.     Large  balloons,   for   hydrogen 
gas,  must  be  made  of  silk,  and  varnished  over  so  as  to  be 
air-tight.     The  car,  or  boat,  is  made  of  wicker-work,  cover-    ; 
ed  with  leather,  well  varnished  or  painted,  and  is  suspended   ; 
by  ropes  proceeding  from  the  net  which  goes  over  the  bal-   ^ 
loon.     The  hydrogen  gas  for  filling  the  balloon  is  procured    : 
by  putting  a  quantity  of  iron-filings,  or  turnings,  with  some   | 
sulphuric  acid  diluted  with  water,  into  casks  lined  with  lead. 
From  the  top  of  these  casks  tin  tubes  proceed,  which  unite 
into  one  that  is  ■  connected  with  the  silk  tube  of  the  balloon,  j 
Balloons  of  oiled  silk  cannot  be  made   smaller  than  five  or  ^ 
six  feet  in  diameter,  as  the  weight  of  the  material  is  too  \ 
great  for  the  air  to  buoy  it  up.  i 

In  1 729,  Bartholomew  Gusman,  a  Jesuit  of  Lisbon,  caus-  \ 
ed  an  aerostatic  machine,  in  the  form  of  a  bird,  to  be  con- 
structed, and  made  it  ascend,  by  means  of  a  fire  kindled  un- 
der it,  in  the  presence  of  the  king,  queen,  and  a  great  con- 
course of  spectators.  Unfortunately,  in  rising,  it  struck 
against  a  cornice,  was  torn,  and  fell  to  the  ground.  The 
inventor  proposed  renewing  his  experiment ;  but  the  people 
had  denounced  him  to  the  inquisition  as  a  sorcerer,  and  he 
withdrew  into  Spain,  where  he  died  in  an  hospital.  In  1766^ 
the  Honourable  Henry  Cavendish  discovered  that  hydrogen, 
gas  (then  called  inflammable  air,)  was  at  least  seven  times 
lighter  than  common  air.     It  occurred  soon  afterwards  to 


AIR   BALLqONS.  167 

the  celebrated  Dr.  Black,  that  if  a  thin  bag  were  filled  with 
this  gaseous  substance,  it  would,  according  to  the  establish- 
ed laws  of  specific  gravity,  rise  in  the  common  atmosphere  ; 
but  he  did  not  pursue  the  inquiry.  The  same  idea  was  con- 
ceived by  Mr.  Cavallo,  to  whom  is  generally  ascribed  the 
honour  of  commencing  the  experiments  on  this  subject.  He 
had  made  but  little  progress,  however,  in  these  experiments, 
when  the  discovery  of  Stephen  and  John  Montgolfier,  paper- 
manufacturers  of  France,  was  announced  in  1782,  and  en- 
gaged the  attention  of  the  philosophical  world.  Observing 
the  natural  ascent  of  smoke  and  clouds  in  the  atmosphere, 
those  artists  were  led  to  suppose  that  heated  air,  if  enclosed 
in  a  suitable  covering,  would  also  prove  buoyant.  After  se- 
veral smaller  experiments,  by  which  this  idea  was  fully  con- 
firmed, they  inflated  a  large  balloon  with  rarefied  air,  which 
immediately  and  rapidly  rose  to  the  height  of  six  thousand 
feet,  and  answered  their  most  sanguine  expectations. 

It  was  soon  found  that  machines  of  this  kind  might  be  so 
contrived,  as  to  convey  small  animals,  and  even  human  be- 
ings, through  the  air  with  ease.  The  first  adventurer  in  this 
aerial  navigation  was  Pilatre  de  Rozier,  a  daring  Frenchman, 
who  rose  in  a  large  balloon  from  a  garden  in  the  city  of  Pa- 
ris, on  the  15th  of  October,  1783,  and  remained  a  consider- 
able time  suspended  in  the  air.  He  made  several  aerial 
voyages  afterwards  of  greater  extent,  and  in  two  of  them  was 
attended  by  other  persons.  In  a  short  time,  however,  the  use 
of  rarefied  air  in  aerostation  was  for  the  most  part  laid  aside, 
as  inconvenient  and  unsafe.  On  recurring  once  more  to  the 
discovery  of  Mr.  Cavendish,  the  philosophers  of  Paris  con- 
cluded that  a  balloon,  inflated  with  hydrogen  gas,  would  an- 
swer all  the  purposes  of  that  contrived  by  the  Montgolfiers, 
and  would  also  possess  several  additional  advantages.  They 
made  their  first  experiment  in  August,  1783,  which  was  at- 
tended with  complete  success.  Since  that  time,  air-balloons 
filled  with  rarefied  air  have  not  been  generally  used. 

The  first  aerial  voyage  in  England  was  performed  by  Vin- 
cent Lunardi,  a  native  of  Italy.  The  diameter  of  his  bal- 
loon was  thirty-three  feet.  Soon  after,  Mr.  Blanchard  as- 
cended, carrying  up  a  pigeon,  which  flew  away  from  the 
boat,  laboured  for  some  time  with  its  wings  to  sustain  itself 
in  the  air,  and  finally  returned  and  rested  on  one  side  of  the 
boat.     He  ascended  so  high  as  to  experience  great  difliculty 


168  DEATH    OF    ROZIER. 

of  breathing,  but  perceiving  the  sea  before  him,  he  descend- 
ed near  Ramsey,  about  seventy-five  miles  from  London,  hav- 
ing travelled  at  the  rate  of  nearly  twenty  miles  an  hour. 

The  singular  experiment  of  ascending  into  the  atmosphere 
with  a  balloon,  and  of  descending  with  a  machine,  called  a 
parachute,  in  the  form  of  a  large  umbrella,  was  performed 
by  Mr.  Garnerin  in  1802.  The  weather  was  clear  and  plea- 
sant, and  the  wind  was  gentle.  In  about  eight  minutes  the 
balloon  and  parachute  had  ascended  to  an  immense  height, 
and  Mr,  Garnerin  in  the  basket,  could  scarcely  be  perceived. 
While  the  spectators  were  contemplating  the  grand  sight 
before  them,  Mr.  Garnerin  cut  the  rope,  and  in  an  instant 
he  was  separated  from  the  balloon,  trusting  his  safety  to  the 
parachute.  Before  the  parachute  opened,  he  fell  with  great 
velocity ;  but  as  soon  as  the  parachute  was  expanded,  which 
took  place  a  few  moments  after,  the  descent  became  very 
gentle  and  gradual.  It  was  observed  that  the  parachute, 
with  the  appendage  of  cords  and  basket  soon  began  to  vi- 
brate like  the  pendulum  of  a  clock,  and  the  vibrations  were 
so  great,  that  more  than  once  the  parachute,  and  the  basket 
with  Mr.  Garnerin,  seemed  to  be  on  the  same  level,  or  quite 
liorizontal ;  the  extent  of  the  vibrations,  however,  diminish- 
ed as  he  descended.  On  corning  to  the  earth,  he  experi- 
enced some  strong  shocks,  but  soon  recovered,  and  remained 
without  any  material  injury. 

The  fate  of  Ilozier,  the  first  aerial  navigator,  and  of  his 
companion  Romain,  has  been  much  lamented.  They  as- 
cended with  an  intention  of  crossing  the  channel  to  England. 
Their  machine  consisted  of  a  spherical  balloon,  filled  with 
hydrogen  gas,  and  under  this  balloon,  a  smaller  one  filled 
with  rarefied  air,  designed  to  diminish  the  specific  gravity 
of  the  whole  apparatus.  For  the  first  twenty  minutes  they 
seemed  to  pursue  the  proper  course  ;  but  the  balloon  ap- 
peared to  be  much  inflated,  and  the  aeronauts  appeared 
anxious  to  descend.  Soon,  however,  when  they  were  at  the 
height  of  three  quarters  of  a  mile,  the  whole  apparatus  was 
in  flames,  and  the  unfortunate  adventurers  fell  to  the  ground, 
and  were  killed. 

The  invention  of  balloons  cannot  be  considered  as  having  / 
added  much  to  the  comfort  or  utility  of  man.  The  only  | 
practical  purposes  which  it  has  been  made  to  subserve,  are  f 
those  of  aiding  meteorological  inquiries,  and  of  inspecting  ; 


NATURAL  HISTORY.  169 

the  fortifications  and  reconnoitring  the  camp  of  an  ehemy, 
which  could  not  be  approached  by  other  means.  The  diffi- 
culties, under  which  this  species  of  navigation  labours,  ap- 
pear at  present  to  be  insurmountable  ;  and  the  want  of  some 
means  to  control  and  regulate  the  movements  of  the  aerial 
vessel  is  so  essential,  as  to  excite  a  fear  that  it  cannot  be  sup- 
plied. 

Questions. — 1.  What  is  aerostation  ?  2.  What  is  the  best  form  for 
a  balloon  ?  3.  What  are  the  two  kinds  of  balloons?  4.  How  is  a 
balloon  filled  with  hydrogen  gas  ?  5.  Who  invented  the  first  agro- 
static  machine,  and  what  was  the  result  ?  6.  What  discovery  did 
Cavendish  make  ?  (Hydrogen  gas  is  14  times  lighter  than  common  air, 
— see  Lesson  on  water.)  7.  Wliat  afterwards  occurred  to  Dr.  Black  .'' 
8.  What  idea  did  Cavallo  conceive  .'' — what  is  ascribed  to  him  .''  9. 
What  discovery  did  the  Montgolfiers  make  ?  10.  Who  was  the  first 
aerial  navigator  ?  11.  What  was  the  next  discovery  in  this  science  ? 
12.  What  is  said  of  the  ascent  of  Mr.  Blanchard  ?  13.  Describe  the 
experiment  of  Mr.  Gamerln.  14.  What  was  the  fate  of  Rozier  and 
Romain  .''  15.  What  is  said  of  the  advantages  which  have  been 
derived  from  balloons  .''  IG.  Of  the  difficulties  under  which  this  spe- 
cies of  navigation  labours.''  [Note.  Small  balloons  may  be  made  of 
thin  strips  of  bladder,  or  otJier  membrane,  glued  together.] 


LESSON  75. 

Natural  History. 
Pellu'cid,  clear,  transparent,  not  opaque. 
Those  who  with  a  philosophical  eye  have  contemplated 
the  productions  of  Nature,  have  all,  by  common  consent,  di- 
vided them  into  three  great  classes,  called  the  Animal,  the 
Vegetable,  and  the  Mineral  or  Fossil  kingdoms.  These 
terms  are  still  in  general  use,  and  the  most  superficial  ob- 
server must  be  struck  with  their  propriety.  Animals  have 
an  organized  structure  which  regularly  unfolds  itself,  and  is 
nourished  and  supported  by  air  and  food  ;  they  consequently 
possess  life,  and  are  subject  to  death ;  they  are  moreover 
endowed  with  sensation,  and  with  spontaneous,  as  well  as 
voluntary,  motion.  Vegetables  are  organized,  supported  by 
air  and  food,  endowed  with  life,  and  subject  to  death  as  well 
as  animals.  They  have  in  some  instances  spontaneous, 
though  we  know  not  that  they  have  voluntary  motion.  They 
are  sensible  to  the  action  of  nourishment,  air,  and  light,  and 
15 


170  NATURAL  HISTORY. 

either  thrive  or  languish  according  to  the  wholesome  or 
hurtful  application  of  these  stimulants.  The  spontaneous 
movements  of  plants  are  almost  as  readily  to  be  observed  as 
their  living  principle.  The  general  direction  of  their  branch- 
es, and  especially  of  the  upper  surface  of  their  leaves,  though 
repeatedly  disturbed,  to  the  light,  the  unfolding  and  closing 
of  their  flowers  at  stated  times,  or  according  to  favourable 
or  unfavourable  circumstances,  with  some  still  more  cu- 
rious particulars,  are  actions  undoubtedly  depending  on  their 
vital  principle,  and  are  performed  with  the  greater  facility 
in  proportion  as  that  principle  is  in  its  greatest  vigour.  Plants 
alone  have  a  power  of  deriving  nourishment,  though  not  in- 
deed exclusively,  from  inorganic  matter,  mere  earths,  salts, 
or  airs,  substances  certainly  incapable  of  serving  as  food  for 
any  animals,  the  latter  only  feeding  on  what  is  or  has  been 
organized  matter,  either  of  a  vegetable  or  animal  nature.  So 
that  it  would  seem  to  be  the  office  of  vegetable  life  alone  to 
transform  dead  matter  into  organized  living  bodies. 

The  Mineral  kingdom  can  never  be  confounded  with  tho 
other  two.  Fossils  are  masses  of  mere  dead  unorganized 
matter,  subject  to  the  laws  of  chemistry  alone  ;  growing  in- 
deed, or  increasing  by  the  mechanical  addition  of  extraneous 
substances,  or  by  the  laws  of  chemical  attraction,  but  not 
fed  by  nourishment  taken  into  an  organized  structure. 
Their  curious  crystallization  bears  some  resemblance  to  or- 
ganization, but  performs  none  of  its  offices,  nor  is  any  thing 
like  a  vital  principle  to  be  found  in  this  department  of  na- 
ture. If  it  be  asked  what  is  this  vital  principle,  so  essential 
to  animals  and  vegetables,  but  of  which  fossils  are  destitute, 
we  must  own  our  complete  ignorance.  We  know  it,  as  we 
know  its  omnipotent  Author,  by  its  effects.  The  infinitely 
small  vessels  of  an  almost  invisible  insect,  the  fine  and  pel- 
lucid tubes  of  a  plant,  all  hold  their  destined  fluids,  convey- 
ing or  changing  them  according  to  fixed  laws,  but  never 
permitting  them  to  run  into  confusion,  so  long  as  the  vita! 
principle  animates  their  various  forms.  But  no  sooner  does 
death  happen,  than,  without  any  alteration  of  structure,  any 
apparent  change  in  their  material  configuration,  all  is  re- 
versed. The  eye  loses  its  form  and  brightness  ;  its  mem- 
branes let  go  their  contents,  which  mix  in  confusion,  and 
thenceforth  yield  to  the  laws  of  chemistry  alone.  Just  so  it 
happens,  sooner  or  later,  to  the  other  parts  of  the  animal  as 


NATURAL    HISTORY.  17*1 

well  as  vegetable  frame.  Chemical  changes  immediately 
follow  the  total  privation  of  life,  the  importance  of  which  be- 
comes instantly  evident  when  it  is  no  more.  If  the  human 
understanding  can  in  any  case  flatter  itself  with  obtaining, 
in  the  natural  world,  a  glimpse  of  the  immediate  agency  of 
the  Deity,  it  is  in  the  contemplation  of  this  i^z^aZ  l^rmapZe, 
which  seems  independent  of  material  organization,  and  an 
impulse  of  his  own  divine  energy. 

The  man  who  surveys  the  vast  field  of  nature,  and  de- 
votes a  portion  of  his  time  to  the  study  of  the  principles 
which  influence,  or  govern,  the  motions  of  animated  beings, 
however  minute  they  may  be,  will  not  only  derive  pleasure 
from  the  pursuit,  but  he  will  gain  the  only  means  of  disco- 
vering the  object  and  utility  oS  their  creation.  And  as  he 
journeys  along  from  one  gradation  of  knowledge  to  another, 
he  will  become  more  and  more  intimate  with  the  designs  of 
the  great  Creator  of  all.  He  will  gain  a  more  comprehen- 
sive view  of  that  wonderful  and  illimitable  power  which  hath 
organized  the  universe,  for  purposes  with  which,  in  the  ful- 
ness of  time,  the  wise  and  the  virtuous  will  doubtless  be 
made  acquainted.  But  knowledge  must  ever  be  progressive ; 
and  he  who  makes  the  attempt  to  read  the  characters  by 
which  the  wisdom,  power,  beneficence,  and  eternal  nature 
of  God  is  stamped  upon  every  thing  here  beloW,  will  not  do 
it  in  vain. 

He  suits  to  nature's  reign  th'  inquiring  eye, 
Skill'd  all  her  soft  gradations  to  descry  ; 
From  Matter's  mode  through  Instinct's  narrow  sway, 
To  Reason's  gradual  but  unbounded  way, 
^      And  sees  through  all  the  wonder-varied  chain 
No  link  omitted,  no  appendage  vain, 
But  all  supporting  and  supported,  till 
The  whole  is  perfect  as  the  Author's  will. 

Hence  even  the  meanest  points  of  Nature's  care 

Fix  his  attention — his  attachment  share  : 

The  pebble,  through  pellucid  waters  shown, 

The  moss  that  clothes — the  shrub  that  cleaves  to  stone, 

The  modest-tinted  flowers  that  deck  the  glade, 

The  aged  tree  that  spreads  its  awful  shade, 

The  feathered  race  that  wing  the  ethereal  way, 

The  insect  tribes  that  float  upon  the  ray, 


172  MINERALOGY. 

The  herds  that  graze,  the  flocks  that  nip  the  plain. 
And  scaly  natives  of  the  watery  reign. 

These  hold  ten  thousand  wonders  to  the  sight, 
Which  prompt  inquiry  and  inspire  delight ; 
Relations — properties — proportions — ends — 
Burst  into  light  as  her  research  extends  ; 
Until  unnumbered  sparks  around  him  fall 
From  the  Great  Source  of  Light,  and  Life,  and  All! 

Dr.  L.  Brown. 

Questions — 1.  How  are  tlie  productions  of  nature  divided?  2. 
What  is  said  of  tlie  organization  of  animals  ?  3.  Of  vegetables  ?  4. 
What  are  fossils  or  minerals  ?  5.  What  do  we  know  of  the  vital 
principle  ? 


LESSON  76. 

3Iinc7'alogy. 

An'alyze,  to  resolve  a  compound  into  its  constituent  parts,  for 
the  purpose  of  examination.  Phys'ical,  natural,  relating  to  na- 
ture. 

All  the  solid  materials  of  which  this  globe  of  ours  is 
composed  have  received  the  name  of  Minerals  ;  and  the  sci- 
ence which  makes  us  acquainted  with  the  relations  under 
which  they  present  themselves  to  us,  is  distinguished  by  the 
title  Mineralogy.  These  substances,  without  doubt,  must 
have  at  all  times  attracted  the  attention  of  mankind  ;  be- 
cause from  them  alone  are  drawn  the  metals,  stones,  and 
other  similar  substances  of  indispensable  use.  But  it  is 
only  very  lately  that  the  method  of  ascertaining  the  compo- 
nent parts  of  these  substances  was  discovered,  or  that  it  was 
possible  to  describe  them  so  as  to  be  intelligible  to  others. 
From  the  ancients  no  information  of  any  consequence  on 
these  topics  is  to  be  expected.  The  whole  science  of  mine- 
ralogy has  been  created  since  the  year  1770,  and  is  at  pre- 
sent advancing  towards  perfection  with  astonishing  rapidity. 
New  minerals  are  every  day  described  and  analyzed,  collec- 
tions are  every  where  forming,  and  travels  of  discovery  are 
succeeding  each  other  without  intermission.  The  fruit  of 
these  labours  has  been  the  discovery  "of  several  new  earths 


MINERALOGY.  173 

and  metals ;  besides  a  vast  number  of  useful  minerals  which 
had  been  formerly  unknown  or  disregarded. 

Nothing  at  first  sight  appears  easier  than  to  describe  a 
mineral,  and  yet  in  reality  it  is  attended  with  a  great  deal 
of  difficulty.  It  is  obvious,  that  to  distinguish  a  mineral 
from  every  other,  we  must  either  mention  some  peculiar  pro- 
perty, or  a  collection  of  properties,  which  exist  together  in 
no  other  mineral.  These  properties  must  be  described  in 
terms  rigidly  accurate,  which  convey  precise  ideas  of  the 
very  properties  intended,  and  of  no  other  properties.  The 
smallest  deviation  from  this  would  lead  to  confusion  and  un- 
certainty. Now  it  is  impossible  to  describe  minerals  in  this 
manner,  unless  there  be  a  peculiar  term  for  each  of  their 
properties,  and  unless  this  term  be  completely  understood. 
Mineralogy,  therefore,  must  have  a  language  of  its  own  ;  that 
is  to  say,  it  must  have  a  term  to  denote  every  mineralogical 
property,  and  each  of  these  terms  must  be  accurately  defin- 
ed. The  language  of  mineralogy  was  invented  by  the  ce- 
lebrated Werner,  of  Freyburg,  and  first  made  known  to  the 
world  by  the  publication  of  his  treatise  on  the  External  Cha- 
racters of  Minerals.  The  object  of  this  philosopher  was  to 
invent  a  method  of  describing  minerals  with  such  precision, 
that  every  species  could  readily  be  recognised  by  those  who 
were  acquainted  with  the  terms  employed.  For  this  pur- 
pose, it  was  necessary  to  make  use  of  those  properties  only 
which  presented  themselves  to  our  senses  on  inspecting  the 
mineral.  These  accordingly  were  chosen,  and  called  by 
Werner  external  characters ;  because  they  may  be  ascer- 
tained without  destroying  the  mineral  examined.  These 
constitute  the  first  division  of  the  characters  of  minerals. 
To  the  second  belong  those  which  are  derived  from  the 
chemical  composition,  or  discovered  by  any  chemical  change 
which  the  mineral  suflfers  ;  to  the  third  are  referred  those 
properties  which  are  afforded  by  certain  physical  characters, 
as  electricity  or  magnetism  ;  and  to  the  fourth  a  few  charac- 
ters, derived  from  circumstances  frequently  observed  with 
regard  to  a  mineral,  as  the  place  where  it  is  found,  or  the. 
minerals  by  which  it  is  usually  accompanied. 

Questions. — 1.    What  are   minerals?     2.  What  is  mineralogy ? 

3.  What  is  said  of  the  knowledge  which  the  ancients  had  of  minerals ," 

4.  What  has  been  the  state  of  this  science  since  the  year  1770  ?    5. 
How  must  minerals  be  described  i    G.  What  was  the  object  of  Werner 

15* 


1T4  CLASSIFICATION    OF    MINERALS, 

in  inventing  the  language  of  mineralogy  ?  7.  What  was  necGssary 
for  this  purpose  ?  8.  Why  \vere  they  called  external  charactera  r  9. 
What  are  the  three  other  divisions  of  the  characters  of  minerals  ?  10. 
What  are  the  general  external  characters  of  minerals  ?  (See  Appen- 
dix.) 11.  -Pa r^icw/arextem^nl  characters  .'  12.  What  farther  descrip- 
tions are  given  f 


LESSON  77. 

Classification  of  Minerals. 

Lap'idary,  one  who  deals  in  gems,  or  precious  stones. 

Ductil'ity,  a  quality  of  certain  bodies,  in  consequence  of  which 
they  may  be  drawn  out  to  a  certain  length  without  fracture. 

Malleabil'ity,  that  property  of  metals  which  gives  thorn  the  capa- 
city of  being  extended  and  flattened  by  hammering. 

Minerals  are  usually  arranged  under  four  classes;  earthy, 
saline,  inflammable,  and  metallic.  The  earthy  minerals  con- 
tain all  such  as  derive  their  qualities  from  the  earths  ;  and 
they  are  divided  into  genera,  according  to  the  particular 
earth  which  predominates  in  each,  or  more  properly,  into 
families,  according  to  their  resemblance  in  external  charac- 
ters, as  the  diamond  family,  the  ruby  family,  talc  family,  and 
others.  The  diamond,  of  which  there  is  only  a  single  spe- 
cies, is  the  hardest  and  most  beautiful  of  all  the  mineral  pro- 
ductions. When  heated  to  the  temperature  of  melting  cop- 
per, and  exposed  to  a  current  of  air,  it  is  gradually  but  com- 
pletely combustible.  It  is  wholly  converted  into  carbonic 
acid,  and  therefore  consists  of  pure  carbon,  as  we  have  al- 
ready mentioned.  By  means  of  diamond  powder,  this  sub- 
stance can  be  cut  and  polished  upon  a  wheel  in  the  same 
way  as  any.  other  gems  are  v/rought  by  emery.  It  is  ma- 
nufactured by  jewellers  into  brilliants  and  rose  diamonds  ; 
and  is  employed  by  glaziers  for  cutting  glass  ;  by  lapidaries 
for  cutting  and  engraving  on  the  hardest  gems,  and  in  the 
finer  kinds  of  clock  work.  Before  the  discovery  of  the 
Brazilian  mines,  diamonds  were  much  more  rare,  and  of 
course  dearer  than  they  have  been  since.  .In  the  year  1730, 
eleven  hundred  and  forty-six  ounces  were  brought  to  Europe  ; 
in  consequence  of  which,  the  price  of  this  article  immedi- 
ately fell  three-fourths,  and  to  prevent  a  still  further  depre- 
ciation, the  Portuguese  government  restricted  the  number 


PLATINA.  175 

of  slaves  allowed  to  be  employed  by  those  to  whom  leases 
of  these  mines  had  been  granted.  The  ruby  family  of  mi- 
nerals is  composed  of  seven  species.  They  are"  all  extreme- 
ly hard,  and  several  of  them  highly  valued  on  account  of 
their  beauty. 

The  saline  minerals  comprehend  all  the  combinations  of 
alkalies  with  acids  which  exist  in  the  mineral  kingdom  : 
such  are  salt-petre  or  nitrate  of  potash  ;  common  rock  salt, 
or  muriate  of  soda;  and  sal-ammoniac,  or  the  muriate-of 
ammonia.  Common  salt  is  found  in  immense  masses  under 
the  earth's  surface  in  many  countries,  particularly  in  Poland, 
Hungary,  and  England.  The  salt-springs  in  some  parts  of 
the  United  States  owe  their  origin  to  beds  of  fossil  salt. 
The  rain-water,  which  penetrates  to  their  surface,  effects  the 
solution  of  a  certain  portion  of  them  with  which  it  comes  in 
contact,  and  thus  becomes,  in  some  cases,  it  is  said,  ten  times 
Salter  than  the  water  of  the  sea.  The  injiammable  minerals 
comprehend  all  combustible  bodies,  except  metals  and  the 
diamond ;  and  include  sulphur,  resins,  bitumens,  and  gra- 
phite. Among  the  bitumens  are  found  the  several  varieties 
of  mineral  coal  that  are  used  for  fuel,  gas-lights,  and  other 
purposes.  At  Pittsburgh  in  Pennsylvania  there  are  inex- 
haustible quantities  of  coal  of  a  superior  quality  ;  it  is  found 
also  in  other  parts  of  the  state,  in  some  parts  of  New- York, 
and  in  Rhode-Island.  It  not  only  enhances  the  value  of  the 
lands  in  which  it  is  found,  and  through  which  it  must  pass, 
but  is  a  source  of  national  wealth.  In  England  there  are 
vast  beds  of  coal  which  often  lie  at  the  depth  of  a  hundred 
feet  beneath  the  surface  of  the  earth.  Near  White-haven 
there  are  some  coal  mines  that  extend  half  a  mile  under  the 
sea. 

The  metallic  minerals  comprehend  all  the  mineral  bodies, 
that  are  composed  either  entirely  of  metals,  or  of  which 
metals  constitute  the  most  considerable  and  important  part. 
It  is  from  the  minerals  belonging  to  this  class  that  all  metals 
are  extracted  ;  and  for  this  reason  they  have  been  called 
ores.  They  are  found  in  a  native  state,  either  simple,  con- 
sisting only  of  one  substance,  or  compound,  when  composed 
of  two  or  more  substances.  We  shall  briefly  describe  a  few- 
of  the  most  useful  metals.  The  first  is  platina.  This  is  the 
heaviest  of  metals,  and  is  found  among  the  gold  ores  of  South 
America  in  the  form  of  small  grains  or  scales.     Its  colour  is 


176^ 


GOLD. 


between  steel-grey  and  silver-white,  and  its  ductility  and 
malleability  arc  very  great.  From  late  improvements  in  the 
process  of  bringing  it  to  a  pure  and  malleable  state,  its  price 
has  been  diminished,  and  its  utility  is  becoming  more  gene- 
rally acknowledged.  Facts  are  continually  brought  to  light 
by  means  of  platina  instruments,  which^  without  it,  might 
perhaps  ever  have  escaped  notice. 

Questions. — 1.  What  are  the  four  classes  of  minerals?  2.  What 
are  earthy  minerals  and  how  are  they  divided  ?  3.  What  is  said  of 
the  diamond  ?  4.  What  are  saline  minerals  ?  5.  Inflammable  ?  6. 
Metallic  ?  7.  To  what  do  salt-springs  owe  their  origin  ?  8.  What  is 
said  of  mineral  coal  ?  0.  What  is  said  of  platina  ?  [Note.  The 
United  States  possess  abundant  sources  of  some  of  the  most  useful 
minerals,  and  of  the  stones  used  in  jewelry.] 


LESSON  78. 

Gold. 

In'got,  a  mass  of  metal.  Nitro-muriafic  acid  is  formed  by  mixing 
one  part  of  nitric  and  four  parts  of  muriatic  acid  ;  it  was  known 
to  the  ancient  alchymists,  and  called  aqua  regia. 

Gold  is  never  found  in  a  mineralized  state  ;  but  it  occurs 
native  in  many  parts  of  the  world,  generally  alloyed  with  a 
little  silver  or  copper,  and  commonly  in  the  form  of  grains. 
Most  of  the  gold  of  commerce  is  obtained  at  present  from 
Africa  and  the  continent  of  America.  It  is  the  heaviest  of 
all  metals  except  platina,  and  although  its  tenacity  is  such 
that  a  wire  of  one  tenth  of  an  inch  in  diameter  will  support  a 
weight  of  five  hundred  pounds  without  breaking,  yet  it  possess- 
es less  tenacity  than  iron,  copper,  platina,  or  silver.  It  is  duc- 
tile and  malleable  beyond  any  known  limits.  The  method 
of  extending  it  used  by  gold-beaters,  consists  in  hammering 
a  number  of  thin  rolled  plates  between  skins  or  animal  mem- 
branes, upon  blocks  of  marble  fixed  in  wooden  frames.  A 
grain  of  gold  has  been  extended  to  more  than  forty-two 
square  inches  of  leaf,  and  an  ounce,  which,  in  the  form  of 
a  cube,  is  not  half  an  inch  either  high,  broad,  or  long,  is 
beaten  under  the  hammer  into  a  surface  of  one  hundred  and 
forty-six  and  a  half  square  feet.  There  are  gold  leaves  not 
thicker  in  some  parts  than  the  three  hundred  and  sixty- 
thousandth  part  of  an  inch ;  but  on  the  wire  used  by  the 


GOLD.  ITTf 

lace-makers  it  is  still  thinner.  An  ingot  of  silver,  usually 
about  thirty  pounds  weight,  is  rounded  into  a  cylinder,  an 
inch  and  a  half  in  diameter,  and  twenty-two  inches  long. 
Two  ounces  of  gold  leaf  are  sufficient  to  cover  this  cylinder, 
and  sometimes  it  is  effected  with  a  little  more  than  one. 
The  ingot  is  repeatedly  drawn  through  the  holes  of  several 
irons,  each  smaller  than  the  other,  till  it  be  finer  than  a  hair  ; 
and  yet  the  gold  covers  it,  and  never  leaves  the  minutest 
part  of  the  silver  bare,  even  to  the  microscope.  It  has  been 
calculated,  that  it  would  take  fourteen  millions  of  films  of 
gold,  such  as  is  on  some  fine  gilt  wire,  to  make  up  the  thick- 
ness of  one  inch:  whereas  fourteen  mi41ion  leaves  of  com- 
mon printing  paper  would  occupy  nearly  three-fourths  of  a 
mile  in  thickness.  The  ductility  of  gold  is  such,  that  one 
ounce  of  it  is  sufficient  to  gild  a  silver  wire  more  than  thir- 
teen hundred  miles  long. 

Gold  may  be  disisolved  in  nitro-muriatic  acid  ;  and  it  thus 
becomes  muriate  of  gold,  which  is  obtained  in  small  crystals, 
and  is  very  soluble  in  water.  If  white  satin  riband,  or  silk, 
be  moistened  with  a  diluted  solution  of  gold,  and,  while 
moist,  exposed  to  a  current  of  hydrogen  gas  or  sulphurous 
acid  gas,  the  metal  will  immediately  be  reduced,  and  the 
silk  become  gilt  with  a  regular  coat  of  gold.  The  potters 
dissolve  gold  to  be  applied  to  the  common  kind  of  porcelain, 
and  it  is  used  in  a  state  of  solution  for  staining  ivory  and 
ornamental  feathers.  It  gives  a  beautiful  purple  red,  which 
cannot  be  effaced  ;  even  marble  may  be  stained  with  it. 
Mercury  and  gold  form  a  compound  called  the  amalgam  of 
gold,  which  is  mucli  used  in  gilding.  The  amalgam  is 
spread  upon  the  metal  which  is  to  be  gilt ;  and  then,  by  the 
application  of  a  gentle  and  equal  heat,  the  mercury  is  driven 
off,  and  the  gold  left  adhering  to  the  metallic  surface. 

Questions. — 1.  In  what  state  is  gold  found  ?  2.  Wliat  is  said  of 
its  weight  and  tenacity  ?  3.  How  do  gold-beaters  extend  it  ?  4. 
What  surface  may  an  ounce  be  made  to  cover  ?  5.  Ho\y  is  silver  wire 
gilt  ?  6.  What  calculation  has  been  made  respecting  the  films  of  gold 
on  gilt  wire  ?  7.  What  length  of  silver  v/ire  may  be  covered  with  an 
ounce  of  gold?  8.  To  what  uses  may  muriate  of  gold  be  applied? 
9v  What  is  amalgam  of  gold,  and  how  is  it  used  in  gilding  ? 


178  SILVER. 


LESSON  79. 

Silver  and  Mercury. 

Ful'minate,  to  explode  with  a  loud  report. 

Silver  is  a  heavy,  sonorous,  brilliant,  white  metal,  only 
moderately  hard,  but  exceedingly  ductile,  and  of  great  mal- 
leability and  tenacity.  It  is  found  in  various  parts  of  the 
world,  particularly  in  Peru  and  Mexico,  in  a  metallic  state  : 
also  in  the  state  of  an  alloy,  of  a  sulphuret,  of  a  salt,  and  in 
that  of  an  oxyd.  It  is  the  most  brilliant  of  metals,  and 
nothing  surpasses  it  in  splendour  except  highly  polished  steel. 
It  is  chiefly  used  for  ornamental  work,  for  domestic  utensils, 
and  for  current  coin  :  but  for  these  purposes  it  is  generally 
alloyed  with  copper,  without  which  it  would  not  have  suf- 
ficient hardness  to  sustain  much  wear.  You  may  know 
when  silver  is  pure  by  hreating  it  in  a  common  fire,  or  in  the 
flame  of  a  candle  ;  if  it  be  alloyed,  it  will  become  tarnished  ; 
but  if  it  be  pure  silver,  it  will  remain  perfectly  white.  Of 
the  salts  of  silver  the  nitrate  is  best  known,  and  when  melted 
and  run  in  moulds,  it  forms  the  lunar  caustic  of  the  apothe- 
cary. A  solution  of  it  mixed  with  a  little  gum  water,  forms,  in 
conjunction  with  an  alkali,  the  indelible  ink,  used  in  marking 
linen. 

Silvering  may  be  performed  on  the  same  substances,  and 
by  similar  methods  with  gilding.  But  as  works  of  this  kind 
are  liable  to  tarnish,  they  are  seldom  used.  Plating  with 
silver  is  performed  in  the  following  manner :  one  of  the  sur- 
faces of  an  ingot  of  copper  is  rendered  smooth  and  clean, 
and  is  sprinkled  over  with  a  saturated  solution  of  borax ; 
upon  this  is  laid  a  plate  of  fine  silver,  about  one  twelfth  the 
weight  of  the  copper,  and  the  two  are  carefully  bound  to- 
gether by  wire.  The  mass  is  now  exposed  to  a  full  red  heat, 
and  the  silver  adheres  to  the  copper.  The  ingot  is  then 
passed  through  a  rolling-press,  and  formed  into  a  plate; 
both  the  silver  and  copper  extending  uniformly  during  the 
whole  process,  at  the  conclusion  of  which,  the  two  metals 
are  inseparably  united. 

Mercury  or  quicksilver  has  been  known  from  the  earliest 
ages  of  the  world.  In  the  temperature  of  our  atmosphere, 
it  is  a  white  fluid  metal,  having  the  appearance  and  brilliancy 


MERCURY.  179 

of  melted  silver.  When  submitted  to  a  sufficient  degree  of 
cold,  it  is  similar  in  appearance  to  other  metals,  and  may  be 
beaten  into  plates.  At  the  poles  it  would  probably  be  al- 
ways solid.  It  readily  combines  with  several  of  the  other 
metals,  and  forms  with  them  what  are  called  amalgams. 
Mercury  is  used  in  large  quantities  for  separating  gold  and 
silver  from  their  ores  ;  for  silvering  mirrors,  for  water-gilding, 
for  making  barometers  and  thermometers  ;  by  the  philoso- 
phical chemist  for  many  purposes  of  the  laboratory ;  and  in 
the  manufactory  of  vermilion.  It  has  also  various  and 
important  uses  in  medicine.  By  dissolving  mercury  in 
nitric  acid,  a  fulminating  powder  is  obtained,  two  or  three 
grains  of  which,  laid  on  an  anvil  and  struck  smartly  with  a 
hammer,  will  explode  with  a  loud  report.  Four  grains  will 
occasion  indentation  in  the  hammer  and  anvil.  By  exposing 
mercury  to  cold  of  a  proper  degree  of  intensity,  which  may 
be  easily  accomplished  by  certain  freezing  mixtures,  it  be- 
comes a  solid  metal.  If  a  lump  of  this  be  dropped  into  a 
cup  of  warm  water,  the  solid  metal  will  immediately  become 
fluid,  and  the  fluid  water  in  the  same  instant  will  become 
solid.  If  a  glass  be  used  for  the  experiment,  it  should  be 
infolded  within  a  cloth  to  prevent  accidents  ;  for  sometimes 
it  will  be  shivered  in  pieces  by  the  rapidity  ©f  the  action. 

The  quicksilver  mine  of  Guanca  Velica,  in  Peru,  is  170 
fathoms  in  circumference,  and  480  deep.  In  this  profound 
abyss  are  seen  streets,  squares,  and  a  chapel.  Thousands  of 
flambeaux  are  continually  burning  to  enlighten  it.  The 
mine  generally  affects  those  who  work  in  it  with  convul- 
sions. Notwithstanding  this,  the  unfortunate  victims  of  an 
insatiable  avarice  are  crowded  together,  and  plunged  naked 
into  these  abysses.  Tyranny  has  invented  this  refinement 
in  cruelty,  to  render  it  impossible  for  any  thing  to  escape  its 
restless  vigilance  : — 

For  in  the  dark  Peruvian  mine  confined, 

Lost  to  the  cheerful  commerce  of  mankind, 

The  groaning  captive  wastes  his  life  away, 

For  ever  exiled  from  the  realms  of  day  ; 

While  all  forlorn  and  sad,  he  pines  in  vain 

For  scenes  he  never  shall  possess  again.    Falconer. 

Questions. — 1.  What  is  silver.?  2.  In  what  states  is  it  found? 
3.  For  what  used  ?  4.  How  can  you  ascertain  its  purity  ?  5.  What  is 
said  of  nitrate  of  silver  ?    C.  Of  silvering  ?    7.  Plating  ?    8.  Describe 


ISO  COPPER. 

mercury.  9.  For  what  is  it  used  ?  10.  What  is  said  of  fulminating 
powder.''  11.  Of  mercury  as  a  solid  metal .-'  12.  What  is  the  descrip- 
tion of  the  quicksilver  mines  in  Peru  ?  13.  How  much  must  the 
temperature  of  mercury  be  reduced  before  it  will  become  solid  ?  (see 
Appendix.)    14.  What  is  said  of  freezing  mixtures  .^ 


LESSON  80. 

Copper  and  Lead. 

Concen'trated,  usually  applied  to  fluids  which  are  rendered  stronger 
by  evaporating,  by  means  of  heat,  a  portion  of  the  water  they 
contain. 

Heteroge'neous,  dissimilar  in  nature.  Homoge'neous,  having  the 
same  nature  or  principles. 

Cu'linary,  relating  to  the.  kitchen. 

Copper  is  a  brilliant  metal,  of  a  red  colour,  very  hard, 
sonorous,  and  elastic  ;  and  the  most  ductile  of  all  the  metals, 
except  gold.  Its  malleability  isalso  so  great,  that  it  is  ham- 
mered into  leaves,  and  sold  in  thin  paper  books  in  imitation 
of  leaf-gold.  It  will  not  burn  so  easily  as  iron  ;  which  is 
evident  from  its  not  striking  fire  by  collision.  On  this  and 
other  accounts  it  has  been  substituted  for  iron  in  the  ma- 
chinery which  i^  employed  in  gun-powder  mills.  The  salts 
of  copper  are  numerous,  and  much  used  in  the  arts  con- 
nected with  chemistry.  Concentrated  sulphuric  acid  dis- 
solves copper  by  the  aid  of  heat,  and  thus  the  sulphate  of 
copper  or  blue  vitriol  is  formed.  Copper  exposed  to  the 
vapour  of  vinegar  or  acetic  acid  becomes  acetate  of  copper 
or  verdigrifS.  All  the  salts  of  copper  are  poisonous,  there- 
fore great  care  should  be  taken  not  to  taste  wantonly  the 
solutions.  The  uses  of  this  metal  are  too  various  to  be  enu- 
merated. Besides  its  employment  to  make  boilers  and  other 
vessels  of  capacity,  and  to  sheathe  the  bottoms  of  ships,  it 
enters  as  a  component  part  into  several  of  the  most 
valuable  alloys.  The  most  important  of  these  alloys  is 
brass,  which  is  formed  by  the  union  of  copper  and  zinc, 
though  brass  is  never  made  with  pure  zinc,  but  generally 
with  calamine,  which  is  a  native  oxyd,  or  rather  carbonate 
of  zinc.  Bronze  and  gun-metal  are  formed  by  the  union  of 
aopper  and  tin  in  the  proportions  of  a  hundred  parts  of  the 
former  to  ten  or  twelve  of  the  latter.  Bell-metal  is  also  an 
alloy  of  tin  with  copper,  but  this  usually  contains  one  fourth 


LEAD.  181 

of  its  weight  of  tin.  Oxyd  of  copper  is  used  by  the  coloured- 
glass  makers.     It  forms  a  beautiful  green  glass. 

Lead  is  a  metal  of  a  bluish  white  colour,  very  brilliant 
when  first  cut  with  a  knife,  but  it  soon  tarnishes  by  ex- 
posure to  the  air ;  it  will  mark  writing-paper,  though  in  a 
fainter  manner  than  plumbago.  It  is  malleable  and  ductile, 
but  possesses  very  little  tenacity.  Lead  may  be  mixed  with 
gold  and  silver  in  a  moderate  heat,  but  when  the  heat  is 
much  increased,  the  lead  rises  to  the  surface,  combined  with 
all  heterogeneous  matters.  Upon  this  property  of  lead  is 
built  the  art  of  refining  the  precious  metals.  If  melted  lead 
be  exposed  to  the  atmosphere,  a  greyish-yellow  powder  be- 
gins to  form  upon  the  surface.  By  keeping  it  exposed  for 
some  time  the  powder  becomes  more  yellow.  In  this  state 
it  is  called  massicot,  or  yellow  oxyd  of  lead.  By  a  second  ex- 
posure this  oxyd  appears  capable  of  combining  with  more 
oxygen.  It  gradually  changes  colour,  and  ultimately  as- 
sumes a  splendid  red.  In  this  state  it  is  called  minium  or 
red  lead.  The  process  requires  considerable  management 
with  regard  to  heat  and  the  access  of  air.  If  the  heat  be 
too  great  or  rapid,  the  lead  becomes  converted  into  a  flaky 
substance,  called  litharge  ;  and  a  still  greater  heat  converts 
it  into  a  clear,  transparent  yellow  glass.  Thin  plates  of  lead, 
exposed  to  the  fumes  of  vinegar  at  a  certain  temperature,  are 
gradually  corroded  and  converted  into  a  heavy  white  pow- 
der, used  as  paint,  and  called  white  lead. 

The  ore  of  lead  is  so  poisonous,  that  the  steam  arising 
from  the  furnaces  where  it  is  worked,  infects  the  grass  in 
all  the  neighbouring  places,  and  kills  the  animals  which  feed 
on  it.  Culinary  vessels,  lined  with  a  mixture  of  tin  and 
lead,  which  is  the  usual  tinning,  are  apt  to  communicate  to 
acid  foods  pernicious  qualities,  and  require  to  be  used  with 
great  caution.  The  same  may  be  said  of  liquors  and  other 
acid  substances  kept  in  glazed  ware,  and  of  wines  adulterat- 
ed with  litharge,  and  such  other  preparations  of  lead  as  are 
sometimes  used  for  the  purpose  of  rendering  them  sweet. 

Questions. — 1.  What  is  copper  ?  2  Why  is  it  substituted  for 
iron  in  some  raacliinery  ?  3.  What  is  Baid  of  the  salts  of  copper  .''  4. 
What  is  brass:  5.  What  are  bronze  and  gun-metal  ?  6.  Bell-inexal? 
7.  Describe  lead?  8.  Why  is  it  used  in  refining  metals?  9.  How 
does  lead  become  oxydized  so  as  to  form  masBicot,  and  minium  ?  10. 
What  is  litharge  ?  il.  How  is  white  lead  formed  ?  12.  What  ip  said 
of  the  poisonous  qtialities  of  lead  ? 
16 


182  IRON. 


LESSON  81. 


Iron  and  Tin. 

Chalyb'eate,  a  term  descriptive  of  those  mineral  waters  which 

are  impregnated  with  iron. 
Pyri'tes,  a  name  given  to  certain  ores,  as  of  iron,  copper,  tin,  &c. 

which  contain  u  large  quantity  of  sulphur,  and  liave  a  metallic 

lustre. 

.  If  utility  were  made  the  standard  of  estimation,  iron 
would  hold  the  first  place  in  the  class  of  metals,  and  would 
be  counted  more  valuable  than  gold,  as  it  appears  indispen- 
sably necessary  to  the  carrying  on  of  every  manufacture. 
It  appears  to  be  one  of  the  principal  means  of  civilizing 
mankind.  There  has  never  been  an  instance  of  a  nation, 
acquainted  with  the  art  of  manufacturing  iron,  which  did 
not  in  time  attain  to  a  degree  of  civilization  infinitely  be- 
yond the  inhabitants  of  those  countries  where  this  metal  was 
wanting,  or  its  use  unknown.  It  is  plentifully  and  univer- 
sally diffused  throughout  nature,  pervading  almost  every 
thing,  and  is  the  chief  cause  of  colour  in  earths  and  stones. 
It  may  be  detected  in  plants  and  in  animal  fluids.  There 
is  a  great  variety  of  iron  ores,  which  have  different  nameS 
given  them  by  the  workmen,  and  are  of  very  different  quali- 
ties. They  are  chiefly  composed  of  the  oxyds  of  iron  and 
clay.  This  metal  is  susceptible  of  two  degrees  of  oxydize- 
ment : — the  scales,  which  are  detached  from  forged  iron  by 
a  high  degree  of  heat,  are  in  the  state  of  black  oxyd,  and  the 
common  rust  of  iron  is  the  red  oxyd.  If  a  bar  of  iron  be 
heated  red-hot,  and  a  stick  of  sulphur  applied  to  it,  a  fluid 
substance  will  drop  from  its  end,  which  is  found  to  be  a  com- 
pound of  sulphur  and  iron,  and  in  chemistry  is  called  sul- 
phuret  of  iron.  Iron-filings  mixed  with  sulphur,  and  made 
into  a  paste  with  water,  in  a  certain  time  become  very  hot, 
and  even  produce  flame.  This  mixture  is  sometimes  buried 
under  the  f.^round  to  produce  an  artificial  volcano.  In  this 
experiment  the  water  is  decomposed,  the  oxygen  unites  with 
the  iron  to  form  an  oxyd  of  iron,  and  with  the  sulphur  to 
form  sulphuric  acid,  while  the  hydrogen  combines  with  ano- 
ther portion  of  the  sulphur,  and  produces  sulphuretted  hy- 
drogen gas,  which  occasions  the  flame.  Green  vitriol  or 
copperas,  which  is  of  so  much  use  in  dyeing,  in  colouring 


ZINC.  183 

hats,  and  in  other  manufactures,  is  a  sulphate  of  iron.  With 
the  prussic  acid,  iron  forms  that  beautiful  paint,  known  in 
commerce  and  the  arts  by  the  name  of  prussian  blue. 

Tin  must  have  been  known  very  early,  as  it  is  mentioned 
by  Homer,  and  also  in  the  books  of  Moses.     It  is  a  white 
metal,  of  little  elasticity,  and  small  specific  gravity.     It  is 
not  very  ductile,  but  so  malleable  tha't  it  «iay  be  beaten  out 
into  leaves  thinner  than  paper.     Tin-foil,  as  it  is  termed,  is 
usually  about  one-thousandth  part  of  an  inch  in  thickness. 
Tin  enters  into  combination  with  many  of  the  metals,  and      . 
forms  alloys  with  them,  some  of  which  are  of  great  impor-   ^ 
tance.     The  amalgam  of  mercury  with  tin  is  used  in  silver- 
ing mirrors.     Pewter,  which  was  formerly  much  used,  is  an  ^ 
alloy  of  tin  and  lead.     In  tinning  iron  the  plates  are  immers-  * 
ed  in  the  melted  tin,  and  are  either  moved  about  in  the  li- 
quid metal,  or  are  dipped  several  different  times.     They  are 
then  taken  out,  and  rubbed   to  remove  the  impurities  from 
the  surface.     Tin  is  consumed  in  large  quantities  by  the 
dyers.     It  is  employed  to  give  a  brightness  to  several  articles 
used  in  forming  reds  and  scarlets.     Substances  which  pro- 
duced to  the  ancients  only  faint  and  fleeting  colours,  give  us 
such  as  are  brilliant  and  durable,  by  the  use  of  a  solution  of 
this  metal. 

Questions. — 1.  What  is  said  of  the  utility  of  iron  ?  2.  Of  its 
abundance  ?  3.  Of  its  oxyds  ?  4.  Of  its  sulphuret  ?  5.  How  may  an 
artificial  volcano  be  produced  ?  5.  How  do  you  account  for  this  ?  7. 
What  is  green  vitriol  and  prussian  blue  ?  8.  Describe  tin.  9.  What 
is  said  of  the  alloys  of  tin  .''  10.  Of  tinning  iron  plates  .''  11.  Of  the 
use  of  tin  by  dyers  ? 


LESSON  82. 

Zinc,  Manganese,  and  Antimony. 

Sublima'tion,  a  process  whereby  certain  volatile  substances  are 
raised  by  heat,  and  again  condensed  by  cold  into  a  solid  form : 
thus  are  obtained  flowers  of  arsenic  and  flowers  of  sulphur. 

Zinc  is  a  very  combustible  metal,  and  when  broken,  ap- 
pears of  a  shining  bluish  white.  It  is  one  of  the  most  abun- 
dant metals  in  nature  except  iron,  and  in  Wales  its  ore  was 
employed  till  lately  in  mending  the  roads.     It  is  used  in 


184  ANTIMONY.  I 

China  for  the  current  coin,  and  for  that  purpose  is  employed  j 

in  the  utmost  purity.     When  zinc  is  heated  it  readily  attracts  ' 

oxygen  ;  and  at  a  white  heat,  the  absorption  of  oxygen  is  so  I 

rapid  and  violent,  that  the  oxyd  immediately  sublimes,  and  ; 

for  this  reason  it  has  acquired  the  name  of  flowers  of  zinc,  i 

It  is  frequently  combined  with  copper  or  tin,  in  various  pro-  '■ 

portions,    and  these  Thixtures  constitute  some  of  the  most  ; 

useful  compound  metals.     It  is  used  in  medicine,  is  the  base  '•■ 

of  white  vitriol,  and  its  carbonate  or  oxyd  may  be  advanta-  ] 
geously  substituted  for  white  lead  in  house-painting. 

Manganese  is  a  brilliant  metal,  of  a  darkish  white  colour, 

inclining  to  gray,  of  considerable  hardness,  and  of  difficult  fu-  I 

sibility.     When  exposed  to  the  air,  it  absorbs  oxygen  with  | 

rapidity  and  falls  into  powder.     It  abounds  in  this  country  ;  l 

but  on  account  of  its  great  affinity  for  oxygen,  it  has  never  i 

been  discovered  in  a  metallic  state.     Its  oxyd  is  easily  pro-  vj 

cured  ;  but  the  pure  metal  can  only  be  obtained  by  art,  and  -4 

in  order  to  preserve  specimens  of  it,  it  is  necessary  to  var-  \ 

nish  them,  or  to  keep  them  immersed  in  oil,  or  ardent  spirits.  1 

Its  oxyds  are  used  in  preparing  the  bleaching  liquor,  in  pu-  i 

rifying  glass,  and  in  glazing  black  earthen  ware.     It  is  also  ] 

employed,  in  some  cases,   to  give  colours  to  enamels  in  the  ; 

manufacture  of  porcelain.     The  black  oxyd  is  much  used  by  ■ 

chemists  for   producing  oxygen    gas,  which,  by  the  applica-  ' 

tion  of  a  red  heat,  it  yields  in  great  abundance.  ] 

Antimony  is  a  brilliant,    brittle  metal,  of  a   silvery  white 

colour,  which  has  not  much  tenacity,  and  is  entirely  desti-  j 

tute  of  ductility.     It  may  be  entirely  volatilized  by  heat.     It  ' 

is  also  susceptible  of  vitrification,  and  produces  a  hyacinth-  j 
coloured  glass.     Antimony   is  combined  with   some  other 

metals  in  making  types  for  printers.     Its  oxyds  are  employ-  J 

ed  in  medicine,  and  in  colouring  glass.  \ 

Arsenic  is  generally  found  in  combination  with  sulphur,  * 

oxygen,  and  many  of  the  metals.     Its  colour  is  bluish,  or  ] 

greenish  white,  becoming,   on   exposure  to  the  air,   dark,  \ 

almost  black ;  it  is  extremely  brittle,  and  at  the  same  time  \ 

the  softest  of  all  metals.     It  is  one  of  the  most  active  of  mi-  [ 

neral  poisons.  * 

Beautiful  shades  of  various  colours  may  be  given  to  diflfe-  y 

rent  substances  by  solutions  of  arsenic.     So  that  the  sub-  I 

stance  which  is  most  injurious  to  the  animal  economy,  ap-  j| 

pears  to  be  endowed  with  properties  for  embellishing  the  J 


STUDY    OF    GEOLOGY.  J 85 

works  of  creation,  and  by  imparting  colour  to  other  bodies, 
is  made  to  minister  in  various  ways  to  our  gratification.  How 
diversified  are  the  means  which  the  Creator  hath  adopted  for 
the  promotion  of  his  benevolent  designs ! 

Who,  not  content 
With  every  food  of  life  to  nourish  man, 
By  kind  illusions  of  the  wondering  sense, 
Has  made  all  nature  beauty  to  his  eye. 
Or  music  to  his  ear.  Akenside. 

Questions. — 1.  What  is  zinc  and  its  uses  ?  2.  Describe  manga- 
nese. 3.  For  wliat  are  its  oxyds  used  .?  4.  What  is  antimony  and  its 
uses  ?  5.  Describe  arsenic.  6.  Give  a  general  account  of  the  seven 
classes  of  metals.  (See  Appendix  to  Lesson  65.)  [Note.  The  de- 
scription of  the  metals  properly  belongs  to  the  subject  of  Chemistry, 
(see  Lesson  65)  but  for  the  sake  of  a  little  more  variety  it  was  thought 
best  to  insert  a  brief  account  of  the  most  important  ones  after  Mine- 
ralogy.] 


LESSON  83. 

Study  of  Geology. 

Crude,  unconnected,  not  well  digested. 
Intersec'tion,  the  point  where  lines  cross  each  other. 

Geology  has  for  its  object  the  study  of  the  earth  in  gene- 
ral, of  its  plains,  hills,  and  mountains  ;  and  embraces  the 
consideration  of  the  materials  of  which  it  is  composed,  and 
the  circumstances  peculiar  to  its  original  formation,  as  well 
as  the  different  states  under  which  it  has  existed,  and  the 
various  changes  which  it  has  undergone.  Geology  has  now 
become  an  object  of  the  attention  and  inquiries  of  many  dis- 
tinguished philosophers.  The  discoveries  of  chemists  and 
mineralogists,  and  the  observations  of  intelligent  travellers, 
have  all  tended  to  facilitate  these  inquiries,  and  to  render 
them  more  enlightened  and  satisfactory  ;  and,  although  mo- 
dern times  have  produced  many  visionary  theories,  and  crude 
conjectures  on  this  subject,  they  have  also  given  birth  to 
some  important  acquisitions,  and  much  correct  philosophy, 
which  will  be  highly  prized  by  all  who  study  the  history  and 
structure  of  our  globe.  The  science  of  geology,  indepen- 
dently of  the  healthy  employment  it  affords,  is  of  great  im- 
portance in  a  practical  point  of  view.  It  very  nearly  con- 
cerns the  miner,  engineer,  and  drainer,  and  even  the  farmer 
16* 


186  GEOLCKJY. 

and  architect ;  and  discloses  a  variety  of  indications  highly 
useful  in  their  respective  pursuits :  to  the  mincr^  the  rocks 
containing  metallic  veins  and  coals  ;  to  the  engineer,  tjie 
association  of  hard  rocks  with  soft ;  to  the  drainer,  the 
intersection  of  a  country  by  hard  dykes,  or  veins  imper- 
vious to  water  ;  to  the  farmer,  the  best  places  for  finding 
lime-stone,  marl,  and  clay ;  and  to  the  arcliilect,  the  most 
durable  stones  for  buildings.  The  person  who  is  attached 
to  .geological  inquiries,  can  scarcely  ever  want  objects  of  em- 
ployment and  of  interest.  The  ground  on  which  he  tread.^ 
— the  country  which  surrounds  him — and  even  the  rocks 
and  stones,  removed  from  their  natural  position  by  art,  are 
all  capable  of  affording  some  degree  of  amusement.  Every 
new  mine  or  quarry  that  is  opened,  every  new  surface  of  the 
earth  that  is  laid  bare,  and  every  new  country  that  is  disco- 
veretl,  offers  to  him  novel  sources  of  information.  In  tra- 
velling, he  is  interested  in  a  pursuit  which  must  constantly 
preserve  the  mind  awake  to  the  scenes  presented  to  it ;  and 
the  beauty,  tlie  majesty,  and  the  sublimity  of  the  great  forms 
of  nature,  oiust  necessarily  be  enhanced  by  the  contempla- 
tion of  their  order,  their  mutual  dependence,  and  their  con- 
nexion as  a  w  hole. 

QuEsTiO.vs. — 1.  What  ig  geology  ?  2.  What  is  said  of  the  discove- 
ries ofcliein'sts  nnd  mineralogists?  3.  Why  is  the  science  of  geolo- 
gy important  in  a  practical  point  of  view  ?  4.  What  are  the  advan- 
tages of  studying  geology  ? 


LESSON  84. 

Geology. 

Stratifica'tion,  the  division  of  a  mass  of  rock  into  many  parallel 
portions,  whose  length  and  breadth  greatly  exceed  t.heir  thick- 
ness.. 

The  surface  of  the  globe,  considered  with  relation  to  its 
inequalities,  is  divided  into  highland,  lowland,  and  the  bot- 
tom of  the  sea.  The  highland  comprises  alpine  land,  com- 
posed of  mountain  groups  or  series  of  mountain  chains  ; 
mountain  chains,  formed  by  a  series  of  those  still  more  simple 
inequalities,  called  mountains:  in  the  former  we  consider 
tlieir  length,  height,  form,  and  connexion  ;  the  parts  of  the 


GEOLOGY.  187 

latter  are  the  foot,  the  acclivity,  and  the  summit.  Lowland 
comprises  those  extensive  flat  tracts  which  are  almost  entirely 
destitute  of  small  mountain  groups.  To  the  bottom  of  the 
sea  belong  the  flat,  the  rocky  bottom,  shoals,  reefs,  and 
islands.  It  is  only  after  a  diligent  study  of  the  inequalities 
just  pointed  out,  that  we  can  with  advantage  undertake  to 
explore  the  means  employed  by  nature  to  produce  them  ;  and 
the  first  step  is  to  proceed  to  the  examination  of  the  physical 
causes  of  the  slow,  but  unceasing  changes  of  the  globe.  Obser- 
vation teaches  us,  that  most  of  the  elevations  and  hollows  we 
meet  with  on  the  surface  of  the  earth  owe  their  origin  to  the 
action  of  the  atmosphere,  to  that  of  the  ocean,  and  to  volca- 
nic fire.  These  powerful  agents  may  be  considered  with 
regard  to  their  destroying,  and,  in  consequence  of  this  de- 
struction, with  regard  to  i\\e\x  forming  effects. 

All  geologists  are  agreed  that  our  present  continents  were 
once  covered  with  water.  This  is  proved  by  the  remains  of 
marine  animals  imbedded  in  the  strata  which  lie  on  the  sum- 
mits of  the  highest  mountains.  The  structure  of  the  globe, 
as  far  as  we  are  acquainted  with  it  from  the  intersections 
made  by  rivers,  by  the  action  of  the  sea  upon  the  coast,  and 
by  mining  operations,  consists  of  beds  of  different  kinds  of 
stone,  which  generally  increase  in  thickness  as  we  descend 
deeper.  Stratification,  in  its  simplest  form,  may  easily  be 
conceived,  by  placing  a  closed  book  with  the  back  resting 
upon  the  table,  and  raising  the  opposite  edges  a  little  ;  the 
book  may  represent  a  thick  mineral  bed,  and  the  leaves  a 
series  of  strata.  In  nature  we  frequently  find  the  strata 
much  broken,  and  thrown  out  of  the  original  position. 
Where  any  series  of  strata  are  wanting,  a  question  naturally 
arises,  have  they  been  carried  away  by  some  sudden  inun- 
dation, before  the  upper  strata  were  deposited,  or  have 
they  never  extended  to  that  place  ?  In  some  instances  it  is 
certain  that  the  strata  have  been  carried  away  from  particu- 
lar situations,  as  in  some  of  the  excavations  which  have 
formed  valleys,  in  which  the  strata  that  terminated  on  one 
side  of  the  valley  may  be  discovered  again  in  the  hills  on 
the  opposite  side.  The  substances  of  which  the  strata  are 
composed,  are  argillaceous,  calcareous,  or  siliceous  earth, 
which  arc  generally  more  or  less  intermixed  or  combined. 
The  strata  of  clay,  or  argillaceous  strata,  being  water-tight, 
give  rise  to  springs,  as  they  arrest  the  water  that  runs  through. 


188  GEOLOGY. 

the  porous  strata,  and  convey  it  to  other  situations.  The 
inclinations  of  the  strata,  with  the  breaks  and  inequalities, 
render  the  globe  habitable,  by  distributing  the  waters  over 
the  surface. 

The  strata  to  a  great  depth  are  generally  characterized 
by  the  remains  of  animals  or  vegetables,  in  what  is  called  a 
petrified  state,  the  organic  structure  being  distinctly  visible, 
although  the  animal  or  vegetable  matter  is  aliTK)st  entirely 
removed,  and  its  place  generally  supplied  by  calcareous  or  sili- 
ceous earth.  These  organic  remains  are  more  abundant  in  the 
upper  than  the  lower  strata ;  and  in  the  lowest  beds  of  rock 
which  have  yet  been  explored,  no  traces  of  organic  existence 
have  been  found.  These  remains  make  us  acquainted  with 
^the  great  changes  which  must  have  taken  place  in  the  con- 
dition of  our  planet  in  remote  ages.  The  uppermost  stratum 
in  England  and  in  various  parts  of  Europe,  is  formed  of  al- 
luvial soil.  In  this  soil,  the  remains  of  quadrupeds  of  vast 
size,  such  as  the  elephant,  the  rhinoceros,  and  mammoth  or 
mastodon,  are  frequently  found.  Many  of  these  are  differ- 
ent from  any  existing  species,  and  they  prove  that  dry  land 
existed  in  the  vicinity,  and  that  Europe  was  then  inhabited 
by  species  of  animals  at  present  unknown. 

The  researches  of  modern  geologists  have  given  abundant 
confirmation  to  the  sacred  history,  not  only  with  respect  to 
the  general  deluge,  but  also  with  regard  to  the  age  of  the 
earth.  Until  very  lately  several  geological  phenomena  were 
considered,  by  superficial  inquirers,  as  indicating  that  the 
creation  of  the  globe  we  inhabit  was  an  event  much  more 
remote  than  the  sacred  history  represents.  This  opinion 
was  kept  in  countenance  only  as  long  as  geology  was  in  its 
infancy.  Every  successive  step  which  has  been  lately  taken 
in  the  improvement  of  this  science  has  served  to  show  its 
fallacy.  The  investigations  of  the  latest  and  most  accurate 
philosophers  have  afforded  the  strongest  proofs,  that  the 
earth,  in  its  present  form,  cannot  have  existed  longer  than 
appears  from  the  Mosaic  account. 

Q,UESTio>fs. — 1.  How  is  the  surface  of  the  globe  divided  ?  2.  What 
does  the  liighland  comprise  ? — lowland?  bottom  of  the  sea  ?  3.  What 
does  observation  teach  us  ?  4.  In  what  are  all  geologists  agreed  ?  5- 
How  is  this  proved  ?  6.  What  is  said  of  the  structure  of  the  globe  .'* 
7.  How  may  stratification  be  conceived  ?  8.  What  are  tiie  substances 
of  which  the  strata  are  composed?  9.  What  is  said  of  organic  re- 
mains ?    10.  What  have  modern  geological  researches  confirmed  ? 


If 


ROCKS.  IbV 

LESSON  85. 

Relative  Situation  of  Rocks. 

Pseu'do,  a  prefix,  which,  put  before  words,  signifies  false,  counter- 
feit. 

Lichen,  (pronounced  Lik'en)  a  cryptogamous  plant,  growing  on 
rocks ;  in  Ireland,  a  species  of  Lichen  is  prepared  and  used  as 
food. 

Presented  to  the  cultured  eye  of  taste, 
No  rock  is  barren,  and  no  wild  is  waste. 

Rocky  masses,  variously  placed  over  each  other,  com- 
pose the  whole  crust  of  the  earth,  to  the  greatest  depth  that 
the  industry  of  man  has  been  able  to  penetrate.  Now  these 
rocks,  with  respect  to  each  other,  occupy  a  determinate 
situation,  which  holds  invariably  in  every  part  of  the  earth. 
Thus  limestone  is  no  where  found  iinder  granite,  but  always 
above  it.  Werner  has  chosen  this  relative  situation  as  the 
basis  of  his  classification  of  rocks.  He  divides  them  into 
five  classes  which  are  called  formations  ;  as  primitive,  transi- 
tion, fletz,  alluvial,  and  volcanic.  The  primitive  formations 
are  of  course  the  lowest  of  all,  and  the  alluvial  constitute  the 
very  surface  of  the  earth ;  for  the  volcanic,  as  is  obvious,  are 
confined  to  particular  points.  Not  that  the  primitive  are 
always  at  a  great  depth  under  the  surface,  very  often  they 
are  at  the  surface  and  constitute  mountains.  In  such  cases 
the  other  classes  of  formations  are  wanting  altogether.  Li 
like  manner  the  transition  and  other  formations  may,  each  ia 
its  turn,  occupy  the  surface,  or  constitute  the  mass  of  a  moun- 
tain. In  some  cases  all  the  subsequent  formations  which 
ought  to  cover  them  are  wanting  in  that  particular  spot. 
Each  of  these  grand  classes  of  formations  consists  of  a  greater 
or  smaller  number  of  rocks,  which  occupy  a  determinate 
position  with  respect  to  each  other,  and  which  like  the  great 
formations  may  often  be  wanting  in  particular  places. 

The  rocks  which  constitute  the  primitive  formations  are 
very  numerous.  They  have  been  divided  into  several  sets, 
such  as  granite,  gniess,  mica-slate,  and  others.  It  deserves 
attention,  that  the  rocks  constituting  them  are  all  chemical 
combinations,  and  generally  crystallized  ;  that  they  contain 
no  petrifactions  ;  and  that  the  oldest  formations  contain  no 
carbonaceous  matter.     Transition   rocks   are   not   so   nu- 


im 


iiocics. 


merous.  In  these,  petrifactions  first  make  their  appearance, 
and  they  usually  consist  of  species  of  corals  and  zoophytes, 
which  do  not  at  present  exist,  and  are  therefore  supposed  to 
be  extinct.  Fletz  rocks  are  disposed  in  flat  or  horizontal 
strata.  They  contain  abundance  of  petrifactions  ;  and  these 
much  more  various  in  their  nature  than  those  which  occur 
in  the  transition  formations,  consisting  of  shells,  fish,  and 
plants.  The  alluvial  formations  constitute  the  great  mass 
of  the  earth's  surface.  They  have  been  formed  by  the  gra- 
dual action  of  rain  and^  river  water  upon  the  other  forma- 
tions. They  consist  of  the  component  parts  of  previously 
existing  rocks,  separated  by  the  influence  of  air,  moisture, 
and  change  of  temperature,  and  deposited  in  beds.  Sand, 
gravel,  loam,  and  petrifactions  of  animals  and  vegetables,  are 
often  found  in  this  class.  Volcanic  formations  are  pseudo- 
volcanic,  or  such  minerals  as  are  altered  in  consequence  of 
the  burning  of  beds  of  coal  situated  in  their  neighbourhood  ; 
and  true  volcanic,  or  such  as  are  actually  thrown  from  the 
crater  of  a  volcano. 

The  expansion  of  water  in  the  pores  or  fissures  of  rocks 
by  heat,  or  congelation,  is  a  physical  cause  of  the  separation 
of  their  parts.  The  solvent  power  of  moisture  exerted  upon 
alkaline  or  calcareous  matter,  in  rocks,  is  another  cause  of 
their  decomposition.  Electricity,  which  is  shown,  by  ex- 
periments with  the  voltaic  apparatus,  to  be  a  most  powerful 
agent  of  decomposition,  seems  to  assist  in  all  these  changes  ; 
electrical  powers  being  almost  constantly  exhibited  in  the 
atmosphere.  The  production  of  a  bed  for  vegetation  is 
effected  by  the  decomposition  of  rocks.  As  soon  as  the  rock 
begins  to  be  softened,  the  seeds  of  lichens,  which  are  con- 
stantly floating  in  the  air,  make  it  their  resting-place.  Their 
generations  occupy  it,  till  a  finely-divided  earth  is  formed, 
which  becomes  capable  of  suppof'ting  mosses  and  heath  : 
acted  upon  by  light  and  heat,  these  plants  imbibe  the 
dew,  and  convert  constituent  pans  of  the  air  into  nourish- 
ment. Their  death  and  decay  afford  food  for  a  more  per- 
fect species  of  vegetable  ;  and,  at  length,  a  mould  is  formed, 
in  which  even  the  trees  of  the  forest  can  fix  their  roots,  and 
which  is  capable  of  rewarding  the  labours  of  the  cultivator. 
The  decomposition  of  rocks  tends  to  the  renovation  of  soils, 
as  well  as  their  cultivation.  Finely-divided  matter  is  carried 
by  rivers  from  the  higher  districts  to  the  low  countries,  and 


LINNiEUS.  191 

alluvial  lands  are  usually  extremely  fertile.  The  quantity 
of  habitable  surface  is  constantly  increased  by  these  opera- 
tions; precipitous  cliffs  are  gradually  made  gentle  slopes, 
lakes  are  filled  up,  and  islands  are  formed  at  the  mouths  of 
great  rivers.  In  these  series  of  changes,  connected  with  the 
beauty  and  fertility  of  the  surface  of  the  globe,  small  quan- 
tities of  solid  matter  are  carried  into  the  sea  ;  but  this  seems 
fully  compensated  for  by  the  effects  of  vegetation  in  absorb- 
ing matter  from  the  atmosphere,  by  the  production  of  coral 
rocks  and  islands  in  the  ocean,  and  by  the  operation  of  vol- 
canic fires. 

What  does  not  fade  1  the  tower,  that  long  had  stood 
The  crash  of  thunder,  and  the  warring  winds, 
Shook  by  the  slow  but  sure  destroyer.  Time, 
Now  hangs  in  doubtful  ruins  o'er  its  base  ; 
And  flinty  pyramids  and  walls  of  brass 
Descend  ;  the  Babylonian  spires  are  sunk  ; 
Achaia,  Rome,  and  Egypt,  moulder  down. 
Time  shakes  the  stable  tyranny  of  thrones, 
And  tottering  empires  rush  by  their  own  weight. 
This  huge  rotundity  we  tread  grows  old  , 
The  sun  himself  shall  die,  and  ancient  night 
Again  involve  the  desolate  abyss.  Armstrong. 

Questions. — 1.  What  is  the  basis  of  Werner's  classification  of 
rocks  ?  2.  Into  what  five  classes  does  he  divide  them  ?  3.  What  is 
said  of  primitive  rocks  ?  4.  Transition  ?  5.  Fletz  ?  6.  Alluvial  ? 
7.  Volcanic?  8.  How  does  the  decomposition  of  rocks  produce  a  bed 
for  vegetation  ?  9.  Tend  to  the  renovation  of  soils  P  [Note.  Some 
knowledge  of  geolog-y  is  daily  becoming  more  necessary,  for  without 
it,  scarce  a  volume  of  travels  or  topography,  a  review  or  a  journal, 
can  be  read  with  all  the  interest  it  demands.  The  structure  of  the 
country  and  the  stratification  of  its  mountains,  are  now  as  often  and  as 
minutely  described,  as  the  plants  and  the  animals  which  are  found 
upon  their  acclivities.]  , 


LESSON  86. 

Biographical  Sketch  of  Linmeus, 

Charles  Linnaeus,  the  founder  of  modern  botany,  was 
born  in  1707,  at  a  small  village  in  Sweden,  where  his  father 


192  LINN.EUS. 

resided  as  a  clergyman.  His  father  was  attached  to  his  gar- 
den, which  he  had  stocked  with  some  of  the  rarer  plants 
in  that  climate,  and  it  is  to  the  delight  with  which  this 
spot  inspired  Charles,  from  his  earliest  childliood,  that  he 
himself  ascribes  his  botanical  passion.  He  was  not  distin- 
guished for  his  proficiency  in  the  ordinary  studies  of  a  lite- 
rary education  ;  but  he  made  a  rapid  progress  in  the  know- 
ledge of  plants,  which  he  ardently  pursued,  both  by  frequent 
excursions  in  the  fields,  and  by  the  unwearied  perusal  of 
such  books  on  the  subject  as  he  was  able  to  procure.  When 
his  father,  who  designed  him  for  his  own  profession,  came 
to  the  seminary,  at  which  he  was  placed,  for  the  purpose  of 
inquiring  into  his  improvement,  he  vvas  much  mortified  to 
find  his  son  declared  utterly  unfit  for  a  learned  profession  by 
the  tutors,  who  advised  that  he  should  be  put  to  some  manual 
occupation.  In  this  perplexity  he  applied  to  the  physician, 
Rothman,  who  was  also  lecturer  in  natural  philosophy.  This 
person  discovered  in  young  Linnaeus,  talents,  which,  though 
not  fitted  to  make  him  a  theologian,  were  not  ill  adapted  for 
another  profession,  and  he  proposed  that  of  a  physician. 
He  took  the  youth  gratuitously  into  his  own  house,  gave 
him  private  instructions,  and  put  him  into  a  systematic  me- 
thod of  studying  botany. 

In  1727,  Linna3us  entered  the' University  of  Lund.  He 
lodged  in  the  house  of  Stoboeus,  a  physician,  who  pos- 
sessed a  good  library,  and  a  museum  of  natural  history.  He 
paid  for  his  entertainment  by  various  little  services,  and  it 
was  only  by  accident  that  his  host  came  to  know  the  extent 
of  his  studious  ardour.  The  mother  of  Stoboeus  having  ob- 
served that  the  candle  in  his  chamber  was  burning  at  unsea- 
sonable hours,  was  induced,  through  fear  of  fire,  to  complain 
of  it  to  her  son.  Stobojus,  therefore,  entered  his  chamber 
at  a  late  hour,  and  found  him  diligently  occupied  with  read-  I 
ing.  Struck  with  this  proof  of  his  thirst  after  improvement, 
he  gave  Linnaeus  the  free  use  of  his  library,  and  admission 
to  his  table.  The  advice  of  Rothman,  however,  caused  him, 
in  1728,  to  quit  Lund,  and  to  remove  to  Upsal,  for  the  sake 
of  the  superior  advantages  it  afforded.  His  father  advanced 
him  the  sum  of  about  eight  pounds  sterling,  which  he  was 
informed  was  all  the  paternal  assistance  he  was  to  expect. 
Thus  he  was  turned  out  upon  the  world  while  yet  but  a  learn- 
er in  the  profession  by  which  he  was  to  obtain  his  bread.  His 


LINN.EUS.  193 

little  patrimony  was  soon  exhausted,  and  he  was  reduced  to 
depend  upon  chance  for  a  meal.  Unable  to  pay  even  for  the 
mending  of  his  shoes,  he  was  obliged  to  patch  them  himself 
with  folded  paper. 

At  length,  in  the  autumn  of  1729,  as  he  was  intently  exa- 
mining some  plants  in  the  garden  of  the  university,  he  was 
accosted  by  Celsius,  professor  of  divinity,  and  an  eminent 
naturalist,  who  was  then  engaged  in  preparing  a  work  on  the 
plants  mentioned  in  the  scripture.  A  little  conversation 
soon  apprised  him  of  the  extraordinary  botanical  acquisitions 
of  the  student,  and  perceiving  his  necessitous  circumstances, 
he  took  him  to  live  in  his  own  house.  It  was  in  this  year 
that  LinnoDus  conceived  the  idea  of  a  new  systematic  ar- 
rangement of  plants.  He  drew  up  a  treatise,  which  was 
shown  to  Celsius,  and  by  him  to  the  botanical  professor,  who 
had  the  liberality  to  bestow  on  it  his  warmest  approbation. 
As  the  professor's  advanced  age  made  him  desirous  of  an  as- 
sistant in  the  office  of  lecturing,  LinnfKus  was  appointed. 
He  was  afterwards  invited  by  the  Academy  of  Sciences  at 
Upsal,  to  explore  the  cold  regions  of  Lapland,  and  the  ala- 
crity with  which  this  proposal  was  accepted,  and  the  faith- 
fulness with  which  the  objects  of  his  journey  were  secured, 
were  equally  creditable  to  his  zeal  and  perseverance.  He 
visited  Holland,  and  the  most  richly  stored  gardens  of  Eng- 
land and  France.  The  great  object  of  his  wishes  had  always 
been  the  professorship  of  botany  at  Upsal,  and  through  the 
kindness  of  an  eminent  Swedish  statesman,  he  at  length 
was  chosen  to  that  station,  and  he  entered  upon  the  duties  of 
his  c^ce  in  the  autumn  of  1741.  His  increasing  fame  at- 
tracted students  from  every  quarter,  among  whom  were  se- 
veral, who  imbibed,  and  diffused  throughout  the  civilized 
world,  a  taste  for  the  science  over  which  Linnaeus  presided. 

His  father  who  had  so  often  grieved  at  the  perverseness  of 
his  son's  disposition  for  hunting  after  plants  and  insects,  for- 
tunately lived  to  see  him,  not  only  professor  of  botany,  but 
dean  of  the  College  of  Physicians  at  Upsal,  caressed  by  the 
noblemen  of  Sweden,  and  honoured  by  all  the  learned  men 
of  Europe.  His  opulence  was  such  as  to  enable  him  to  pur- 
chase an  estate  near  Upsal,  which  was  his  chief  summer  re- 
sidence during  the  last  fifteen  years  of  his  life.  His  views 
of  nature  impressed  him  with  the  most  devout  sentiments 
towards  its  author,  and  a  glow  of  unaifected  piety  is  conti- 
17 


194  STUDY   OP    BOTANY. 

niially  breaking  forth  throughout  his  writings.  A  general 
mourning  took  place  at  his  death,  in  1778,  and  his  body 
was  attended  to  the  grave  with  every  token  of  respect. 

Questions. — 1.  To  what  circumstance  does  Linnaeus  ascribe  his 
passion  for  botany?  2.  What  is  said  of  his  early  proficiency?  3 
How  was  his  thirst  for  improvement  discovered  at  the  University  of 
Lund  ?  4.  What  is  said  of  his  pecuniary  means  on  his  removal  to 
Upsal  ?  5.  In  what  manner  did  he  come  into  notice  at  Upsal  ?  (3. 
By  what  means  was  a  taste  for  natural  history  diffused  throughout  the 
oivilizcd  world  ? 


LESSON  67. 
Study  of  Botany. 

Botany  is  that  branch  of  natural  history  which  treats  of 
the  vegetable  kingdom.  The  study  of  this  science  is  not  a 
trifling  employment,  undeserving  the  time  and  attention  be- 
stowed upon  it.  Can  we  for  a  moment  conceive  that  the 
works  of  God  are  unworthy  the  attention  of  man  ? — that 
those  productions  which  bear  such  evident  marks  of  the  wis- 
dom and  power  of  the  Creator,  are  too  contemptible  for  the 
examination  of  his  creatures  ?  Whoever  has  had  the  curio- 
sity to  crop  the  humblest  flower  of  the  field,  and  to  observe 
the  wonderful  conformation  of  its  parts,  combining  the  unit- 
ed purposes  of  elegance  arid  utility,  will  not  hastily  despise 
the  study  of  nature.  But  when  these  observations  are  ex- 
tended through  the  immense  variety  of  productions  which 
compose  the  vegetable  kingdom  ;  when  the  different  offices 
of  each  particular  part  of  the  plant,  every  one  essentially 
contributing  towards  its  existence  and  propagation,  are  con- 
sidered ;  when  we  advert  to  the  variety  of  modes  by  which 
these  ends  are  effected,  and  the  infinite  contrivance  which 
is  exhibited  in  their  accomplishment,  a  wide  field  for  instruc- 
tion and  admiration  is  opened  before  us. 

We  need  not  labour  to  prove  how  delightful  and  instruct- 
ive it  is  to 

"  Look  through  nature  up  to  nature's  God  ;" 

neither,  surely,  need  we  attempt  to  show,  that  if  any  judi- 
i^ious  or  improved  use  is  to  be  made  of  the  natural  bodies 


Study  of  botany.  195 

around  us,  it  must  be  expected  from  those  who  discriminate 
their  kinds  and  study  their  properties.  Of  the  benefits  of 
natural  science  in  the  improvement  of  many  arts,  no  one 
doubts.  Our  food,  our  medicine,  our  luxuries  are  improved 
by  it.  By  the  inquiries  of  the  curious  new  acquisitions  are 
made  in  remote  countries,  and  our  resources  of  various  kinds 
are  augmented.  We  find  that  gardening,  the  most  elegant, 
and  agriculture,  the  most  useful  of  all  arts,  are  improved  only 
in  those  countries  in  which  botany  is  made  subservient  to 
their  advancement.  And  when  a  knowledge  of  this  science 
is  more  generally  diffused  throughout  our  own  country,  we 
may  expect  to  see  it  more  frequently  enriched  with  fields 
and  adorned  with  gardens,  which  while  they  bestow  hononr 
on  their  possessors,  shall  prove  a  pleasant  recreation  to  the 
old,  and  a  useful  study  to  the  young.  Nor  should  its  influ- 
ence on  the  moral  character  be  disregarded.  The  late  Pre- 
sident Dwight  was  an  eminent  champion  of  the  virtue  which 
he  practised.  He  often  directed  the  attention  of  his  pupils 
to  Sweden,  to  point  out  the  influence  of  natural  history  on 
the  moral  character  of  man.  In  that  country  botany  is 
taught  in  the  schools,  and  the  habitation  of  her  excellent 
children  presents  a  cheering  picture  of  domestic  felicity. 
Their  piety  and  their  patriotism  both  flow  from  the  same 
source;  for  while  they  examine  the  productions  of  their 
country,  they  become  attached  to  its  soil,  and  while  they 
contemplate  the  works  of  their  Maker,  they  are  animated 
with  the  glowing  spirit  of  devotion. 

Botany  deserves  our  highest  regard  as  the  source  of  mental 
improvement.  Nothing  so  powerfully  attracts  the  notice  of 
the  young  observer,  as  the  gay^  though  fleeting  beauty  of 
flowers ;  yet  these  interesting  objects  serve  to  produce  an 
accuracy  of  discrimination,  which  is  the  foundation  of  cor- 
rect taste  and  sound  judgment.  To  those  whose  minds  and 
understandings  are  already  formed,  this  study  may  be  re- 
commended, independently  of  all  other  considerations,  as  a 
rich  source  of  innocent  pleasure.  Some  people  are  ever  in- 
quiring what  is  the  use  of  any  particular  plant  ?  They  con- 
sider a  botanist  with  respect,  only  as  he  may  be  able  to  teach 
them  some  profitable  improvement,  by  which  they  may 
quickly  grow  rich,  and  be  then  perhaps  no  longer  of  any 
use  to  mankind  or  to  themselves.  They  would  permit  their 
children  to  study  botany,  only  because  it  might  possibly  lead 


196  TEXTURE   OF  VEGETABLES. 

to  professorships,  or  other  lucrative  preferment.  These 
views  are  not  blameable,  but  they  are  not  the  sole  end  of 
human  existence.  Is  it  not  desirable  to  call  the  soul  from 
the  feverish  agitation  of  worldly  pursuits,  to  the  contempla- 
tion of  divine  wisdom  in  the  beautiful  economy  of  nature  1 
Is  it  not  desirable  to  walk  with  God  in  the  garden  of  crea- 
tion, and  hold  converse  with  his  providence  ?  If  such  ele- 
vated feelings  do  not  lead  to  the  study  of  nature,  it  cannot 
be  far  pursued  without  rewarding  the  student  by  exciting 
them.  The  more  we  study  the  works  of  the  Creator,  the 
more  wisdom,  beauty,  and  harmony  become  manifest ;  and 
while  we  admire,  it  is  impossible  not  to  adore. 

"  Soft  roll  your  incense,  herbs,  and  fruits,  and  flowers, 

In  mingled  clouds,  to  Him,  whose  sun  exalts, 

Whose  breath  perfumes  you,  and  whose  pencil  paints !" 

Questions. — 1.  What  is  Botany?  2.  Why  is  the  study  of  this 
science  not  a  trifling  employment  ?  3.  What  renders  it  a  field  for  in- 
struction and  admiration  ?  4.  What  may  we  expect  when  a  know- 
ledge of  this  science  is  more  generally  diffused  ?  5.  Why  did  Dr. 
Dwight  often  direct  the  attention  of  his  pupils  to  Sweden  ?  6.  How 
is  botany  a  source  of  mental  improvement  ?  7.  How  do  some  people 
regard  a  botanist  ?  8.  How  are  these  views  to  be  considered,  and  what 
reply  is  made  to  thera  .' 


LESSON  88. 

Texture  of  Vegetables. 

Longitu'dlnally,  running  in  the  longest  direction. 
Concen'tric,  having  one  common  centre. 

Every  part  of  a  living  plant  is  covered  with  a  skin  or  mem- 
brane called  the  cuticle.  In  the  root  and  trunk  it  is  coarse 
and  hard,  while  in  the  leaves,  flowers,  and  tender  shoots, 
it  is  a  fine,  colourless,  and  transparent  film,  not  thicker  than 
a  cobweb.  It  is  porous  and  admits  of  the  passage  of  fluids 
from  within  as  well  as  from  without,  but  in  a  due  and  defi- 
nite proportion  in  every  plant.  It  not  only  protects  the 
young  tree  from  external  injury,  but  it  preserves  our  choicest 
fruit  from  premature  decay,  and  without  it,  the  leaf  would 
lose  its  verdure,  the  flower  its  fragrance,  and  their  transitory 
beauty   would    become  still  more  evanescent.     To  wheat, 


TEXTURE  OF  VEGETABLES.  197 

rye,  and  most  kinds  of  grass,  the  cuticle  is  of  the  highest 
importance,  for  it  supports  their  stalks  and  secures  them  from 
injuries.  In  these,  and  still  more  abundantly  in  some  others, 
Sir  Humphry  Davy  has  discovered  the  existence  of  a  flinty 
earth ;  and  it  is  this  which  makes  the  ashes  of  burnt  straw 
one  of  the  best  materials  which  can  be  employed  in  giving 
its  finest  polish  to  marble.  The  fruit  of  the  peach  and  the 
leaf  of  the  mullein  have  a  cuticle  covered  with  dense  and 
rather  harsh  wool. 

Immediately  under  the  cuticle  of  leaves  and  young  stems 
is  found  a  substance  called  the  cellular  integument.  It  is 
of  a  pulpy  texture  and  the  seat  of  colour.  No  plants  are 
destitute  of  it,  for  it  is  the  seat  of  operations  indispensably 
necessary  to  healthy  vegetation.  When  the  cellular  integu- 
ment is  removed,  the  outer  surface  of  the  hark  presents  it- 
self, which  in  plants  or  branches  that  are  only  one  year  old, 
consists  of  one  simple  layer ;  but  in  the  older  branches  and 
trunks  of  trees,  it  consists  of  as  many  layers  as  they  are 
years  old.  The  bark  contains  a  great  number  of  woody 
fibres,  running  for  the  most  part  longitudinally,  which  give 
it  tenacity,  and  in  which  it  differs  very  essentially  from  the 
parts  already  described.  In  the  bark,  the  peculiar  virtues  or 
qualities  of  particular  plants  chiefly  reside.  Here  we  find 
in  appropriate  vessels  the  resin  of  the  Fir,  the  astringent 
principle  of  the  Oak,  the  fine  and  valuable  bitter  of  the  Pe- 
ruvian Bark,  and  the  exquisitely  aromatic  oil  of  the  Cinna- 
mon. Immediately  under  the  bark  is  situated  the  wood, 
which  forms  the  great  bulk  of  trees  and  shrubs.  When  cut 
across  it  is  found  to  consist  of  numerous  concentric  layers. 
LinnjEus  and  most  writers  believe  that  one  of  these  circular 
layers  is  formed  every  year,  the  hard  external  part  being 
caused  by  the  cold  of  winter  ;  consequently,  that  the  exact 
age  of  a  sound  tree  when  felled  may  be  known  by  counting 
these  rings.  That  the  bark  produces  wood  seems  to  have 
been  proved  beyond  dispute,  for  plates  of  tin-foil  have  been 
introduced  under  the  barks  of  growing  trees,  the  wounds 
carefully  bound  up,  and  after  some  years,  on  cutting  them 
across,  the  layers  of  new  wood  have  been  found  on  the  out- 
side of  the  tin. 

The  centre  or  heart  of  the  vegetable  body,  within  the 
wood,  contains  the  pith.  Its  texture  is  precisely  similar  to 
that  of  the  cellular  integument,  being  composed  of  cells 


198  SAP  AND  SECRETIONS. 

wliich  are  seen  to  best  advantage  in  the  centre.  These 
cells,  which  are  unusually  large  in  the  Elder,  are  filled  with 
fluids  when  young,  but  in  old  branches  the  fluids  are  gone 
and  the  cells  are  empty.  Of  its  uses  in  the  economy  of 
vegetation,  but  little  is  known. 

Questions. — 1.  What  is  the  cuticle  of  a  plant  ?  2.  How  is  it  de- 
scribed and  what  are  its  uses  ?  3.  Describe  the  cellular  integument. 
4.  Tho  bark.  5.  The  wood.  6.  The  pith.  7.  What  chiefly  resides 
in  the  bark  of  plants  .''  8.  What  is  said  of  the  circular  layers  of  wood  ? 
9.  How  has  R  been  shown  that  the  bark  produces  the  wood .' 


LESSON  89. 

Sap  mid  Secretions. 

Odoriferous,  fragrant,  perfumed.     Propnl'sion,  the  act  of  driving 
forward.     Es'culent,  good  for  food,  eatable. 

That  the  whole  vegetable  body  is  an  assemblage  of  tubes 
and  vessels  is  evident  to  the  most  careless  observer ;  and 
those  who  are  conversant  with  the  microscope  and  book* 
relating  to  it,  have  frequent  opportunities  of  observing  how 
curiously  these  vessels  are  arranged,  and  how  different  spe- 
cies of  plants,  especially  trees,  differ  from  each  other  in 
the  structure  and  disposition  of  them.  It  is  familiar  to  every 
one  that  plants  contain  various  substances,  as  sugar,  gum, 
acids,  odoriferous  fluids,  and  others,  to  which  their  various 
flavours  and  qualities  are  owing  f  and  a  little  reflection  will 
satisfy  ua  that  such  substances  must  each  be  lodged  in  proper 
cells  and  vessels  to  be  kept  distinct  from  each  other.  They 
are  extracted,  or  secreted,  from  the  common  juice  of  the 
plani,  and  called  its  peculiar  or  secreted  fluids.  Various 
experiments  and  observations  prove  also  that  air  exists  in 
the  vegetable  body,  and  must  likewise  he  contained  in  ap- 
propriate vesaels.  Besides  these,  we  know  that  plants  arc 
nourished  and  invigorat,ed  by  water,  which  they  readily  ab- 
sorb, and  which,  by  proper  tubes  or  vessels,  is  quickly  con- 
veyed through  their  stalks  and  leaves.  It  is  observed, 
moreover,  that  all  plants,  as  far  as  any  experiment  has  been 
raade,  contain  a  common  fluidj  which  at  certain  seasons  of 
the  year  Is  to  be  obtained  in  great  quantity,  and  this  is  proper- 


SAP  AND  SECRETIONS.  199 

\y  called  the  sap.  It  is  really  the  blood  of  the  plant,  by 
which  its  whole  body  is  nourished,  and  from  which  the  pecu- 
liar secretions  are  made. 

The  great  motion,  called  the  flowing  of  the  sap,  which  is 
to  be  detected  principally  in  the  spring,  and  slightly  in  the 
autumn,  is  totally  different  from  that  constant  propulsion  of 
it  which  is  going  on  in  every  growing  plant.  Its  facility  to 
run  is  the  first  step  towards  the  revival  of  vegetation  from 
the  torpor  of  winter.  Its  exciting  cause  is  heat,  and  the  ef- 
fect of  heat  is  in  proportion  to  the  degree  of  cold  to  which  the 
plant  has  been  accustomed.  The  same  principle  accounts 
for  the  occasional  flowing  of  the  sap  in  autumn  after  a  slight 
frost.  Such  a  premature  cold  increases  the  sensibility  of 
the  plant  to  any  warmth  that  may  follow,  and  produces,  in  a 
degree,  the  same  state  of  its  constitution  as  exists  after  the 
long  and  severer  cold  of  winter. 

The  sap  in  its  passage  through  the  leaves  and  bark  be- 
comes quite  a  new  fluid,  possessing  the  peculiar  flavour  and 
qualities  of  the  plant,  and  not  only  yielding  woody  matter 
for  the  increase  of  the  vegetable  body,  but  furnishing  various 
secreted  substances.  These  are  chiefly  found  in  the  bark, 
and  often  in  large  and  conspicuous  vessels,  as  the  turpen- 
tine-cells of  the  Fir  tribe.  In  herbaceous  plants,  whose 
stems  are  only  of  annual  duration,  the  perennial  roots  fre* 
quently  contain  these  fluids  in  the  most  perfect  state,  nor 
are  they,  in  such,  confined  to  the  bark,  but  deposited  through- 
out the  substance  of  the  root,  as  in  Rhubarb  and  Gentian. 
It  may  be  useful  to  enumerate  some  of  the  most  distinct  se- 
cretions of  vegetables.  Gum  or  mucilage,  a  viscid  sub- 
stance of  little  flai'our,  exudes  from  many  trees  in  the  form 
of  large  drops  or  lumps,  as  in  Plum,  Cherry,  and  Peach  trees. 
Resin  is  a  substance  soluble  in  spirits,  and  it  differs  ac- 
cording to  the  peculiar  tree  from  which  it  is  obtained.  The 
more  refined  and  volatile  secretions  of  a  resinous  nature  are 
called  essential  oils,  and  they  are  often  highly  aromatic  and 
odoriferous.  They  exist  in  the  highest  perfection  in  the 
perfumed  effluvia  of  flowers,  some  of  which,  capable  of 
combination  with  spirituous  fluids,  are  obtainable  by  dis- 
tillation, as  that  of  the  Lavender  and  Rose.  The  bitter 
secretion  of  many  plants  does  not  seem  exactly  to  accord 
with  any  of  the  foregoing.  Some  facts  would  seem  to 
prove   it  of  a  i^sinous  nature,   but  it   is  often  perfectly 


200  PROCESS  OF  VEGETATION. 

soluble  in  water  like  gum  or  mucilage.  Acid  secretions 
are  well  known  to  be  very  general  in  plants.  The  astrin- 
gent principle  would  seem  to  be  a  sort  of  acid,  of  which 
there  are  many  different  forms,  or  kinds,  and  among  them 
the  tanning  principle  of  the  Oak,  Willow,^  and  others.  To 
the  secretion  of  plants  we  owe  the  existence  of  sugar.  In 
tropical  countries  it  is  commonly  obtained  from  the  ex- 
pressed juice  of  the  sugar-cane,  but  the  Maple  of  the  North 
yields  it  equally  pure  and  scarcely  less  abundant.  It  exists 
also  in  the  roots  of  some,  and  in  the  esculent  fruit  of  many 
plants,  communicating  a  sweet  and  usually  an  agreeable 
taste. 

To  the  foregoing  secretions  of  vegetables  may  be  added 
those  on  which  their  various  colours  depend.  We  can  but 
imperfectly  account  for  the  green  so  universal  in  their 
herbage,  but  we  may  gratefully  acknowledge  the  beneficence 
of  the  Creator  in  clothing  the  earth  with  a  colour  the  most 
pleasing  and  the  least  fatiguing  to  our  eyes.  We  may  be 
dazzled  with  the  brilliancy  of  a  flower-garden,  but  we  repose 
at  leisure  on  the  verdure  of  a  grove  or  meadow. 

Questions. — 1.  What  is  said  of  the  whole  vegetable  body?  2. 
What  ere  called  the  peculiar  or  secreted  fluids  of  plants?  3.  What  i« 
said  of  the  sap  ?  4.  The  Jlowing  of  the  sap  ?  5.  What  are  some  of 
the  most  distinct  secretions  of  vegetables  ?  0.  What  is  said  of  those  se- 
cretions on  which  the  colours  of  vegetables  depend  ? 


LESSON  90. 

Process  of  Vegetation. 
Incip'ient,  just  beginning.  Suc'culent,  juicy,  moist. 
When  a  seed  is  committed  to  the  ground,  it  swells  by  the 
moisture  which  its  vessels  soon  absorb,  and  which,  in  con- 
junction with  some  degree  of  heat,  stimulates  its  vital  prin- 
ciple. Atmospherical  air  is  also  necessary  to  incipient 
vegetation,  for  seeds  in  general  will  not  grow  under  water, 
except  those  of  aquatic  plants,  nor  under  an  exhausted  re- 
ceiver. Seeds  buried  in  the  ground  to  a  greater  depth  than 
is  natural  to  them,  do  not  vegetate,  but  they  often  retain  the 
power  of  vegetation  for  an  unlimited  period.  Earth  taken 
from  a  considerable  depth  will,  when  exposed  to  the  air,  be 


PROCESS  OF  VEGETATION.  J^Ol 

soon  covered  with  young  plants,  though  no  seeds  have  been 
allowed  to  have  access  to  it.  The  young  root  is  the  first 
part  of  the  infant  plant  that  comes  forth,  and  by  an  unerring 
law  of  nature,  it  is  sent  downwards,  to  seek  out  nourishment 
as  well  as  to  fix  the  plant  to  the  ground.  In  sea-weeds,  it 
seems  merely  to  ansv.^er  the  latter  purpose.  In  the  Dod- 
der, the  original  root  lasts  only  till  the  stems  have  established 
themselves  on  some  vegetable,  on  whose  juices  they  feed  by 
means  of  other  roots  or  fibres,  and  then  it  withers  away. 
When  the  young  root  has  made  some  progress,  the  two  lobes, 
commonly  of  a  hemispherical  figure,  which  compose  the 
chief  bulk  of  the  seed,  swell  and  expand,  and  are  raised  out 
of  the  ground  by  the  ascending  stem.  These  lobes  are 
called  the  Cotyle'dons,  and  between  them  is  seated  the  Em- 
hryo,  or  germ  of  the  plant.  The  leaves  of  the  germ  being 
of  a  succulent  nature,  assist  the  plant  by  attracting  from  the 
atmosphere  such  particles  as  the  tender  vessels  are  fitted  to 
convey.  These  particles,  however,  have  not  in  their  own 
nature  a  sufficiency  of  nutriment  for  the  increasing  plant. 
The  substance  or  farina  of  the  lobes  becomes  soft  and  sweet, 
being  converted  into  sugar,  and  is  conveyed  as  long  as  it 
lasts  to  the  tender  plant,  by  means  of  innumerable  small 
vessels,  which  are  spread  through  the  lobes  ;  and  vi^hich, 
uniting  into  one  common  trunk,  enter  the  body  of  the  germ, 
and  thus  supply  that  balmy  liquor,  without  which  the  plant 
must  inevitably  have  perished  ;  its  root  being  then  too  small 
to  absorb  a  sufficiency  of  food,  and  its  body  too  weak  to  as- 
similate it  into  nourishment. 

Such  is  the  general  course  of  vegetation  in  plants  furnished 
with  two  lobes  or  cotyledons.  But  there  is  a  very  distinct 
tribe,  which  have  but  one  lobe,  and  are  called  monocoty- 
le'dons.  These  are  the  grass  and  grain  tribe,  and  many 
others,  in  which  the  body  of  the  seed  does  not  ascend  out 
of  the  ground.  The  preservation  of  the  vital  principle  in 
seeds  is  one  of  those  wonders  of  nature  which  pass  unre- 
garded, from  being  every  day  under  our  notice.  Some  may 
be  sent  round  the  world  through  every  vicissitude  of  climate, 
or  be  buried  for  ages  deep  in  the  ground,  and  yet,  in  favour- 
able circumstances,  they  will  vegetate.  Others  in  order  to 
succeed  must  sow  themselves,  in  their  own  way,  and  at  their 
own  time.  Great  degrees  of  heat,  short  of  boiling,  do  not  im- 
pair their  vegetative  power,  nor  do  we  know  any  degree  of 


202  ROOTS. 

cold  that  has  such  an  effect.  Those  who  convey  seeds  from  dis- 
tant countries,  should  be  instructed  to  keep  them  dry  ;  for  if 
they  receive  any  damp  sufficient  to  cause  an  attempt  at  vege- 
tation, they  necessarily  die,  because  the  process  cannot,  as  they 
are  situated,  go  on.  It  is  usual  with  gardeners  to  keep  melon 
and  cucumber  seeds  for  a  few  years,  in  order  that  the  future 
plants  may  grow  less  luxuriantly,  and  be  more  abundant  in 
blossoms  and  fruit.  Dr.  Darwin  accounts  for  this  from  the 
damage  which  the  lobes  may  receive  from  keeping,  by  which 
their  power  of  nourishing  the  infant  plant,  at  its  first  ger- 
mination, is  lessened,  and  it  becomes  stinted  and  dwarfish 
through  its  whole  duration. 

Questions. — 1.  What  takes  place  when  a  seed  is  committed  to  the 
ground?  2.  What  is  said  of  the  young  root  ?  3.  Of  sea-weeds?  4. 
Of  Dodder  ?  5.  What  are  the  two  lobes  called  ?  6.  The  germ  ?  7. 
How  do  the  leaves  of  the  germ  assist  the  plant  ?  8.  To  what  use  is  the 
farina  of  the  lobes  applied  ?  9.  What  are  plants  called  that  have  only 
one  lobe  ?  10.  What  is  said  of  the  preservation  of  the  vital  principle 
in  see^?  ?  11.  Why  do  gardeners  sometimes  keep  melon  and  cucum- 
ber seeds  for  a  few  years  ?    12.  How  does  Dr.  Darwin  account  for  this  ? 


LESSON  91. 

Roots,  Ste7ns,  Buds,  and  Leaves. 

Rad'icle,  the  minute  branch  of  a  root. 

Physiology,  the  doctrine  of  the    constitution  of  the 

nature. 
Pcrs]>ire',  to  give  out  moisture.     Absorb',  to  take  in  moisture* 

The  root  of  a  plant  consists  of  two  parts,  the  body  of 
the  root,  and  the  fibre.  The  latter  only  is  essential,  being 
the  part  which  imbibes  nourishment.  Roots  are  either  of 
annual,  biennial,  or  perennial  duration.  The  first  belong  to 
plants  which  live  only  one  year,  or  rather  one  summer,  as 
barley;  the  second  to  such  as  are  produced  one  season,  and, 
living  through  the  ensuing  winter,  produce  flowers  and  fruit 
the  following  summer,  as  winter-rye  and  wheat ;  and  the  third 
to  those  which  live  and  blossom  through  many  succeeding 
seasons  to  an  indefinite  period,  as  trees  and  many  herbaceous 
plants.  Botanists  distinguish  several  different  kinds  of  roots, 
which  are  necessary  to  be  known,  not  only  for  botanical 
purposes,  but  as  being  of  great  importance  in  agriculture  and 


LEAVES.  203 

gardening.  Barren  and  thin  soils  are  best  suited  to  the 
wide  spreading  roots,  which  creep  extensively  on  the  surface ; 
dry  and  sandy  plains  are  adapted  to  those  which  penetrate 
deep  for  nourishment,  and  are  supplied  with  bulbs  for  its 
preservation,  or  with  downy  radicles  for  its  abundant  ab- 
sorption. 

Linnaius  enumerates  seven  kinds  of  trunks,  stems,  or 
stalks  of  vegetables.  These  are  necessary  to  be  known  for 
botanical  distinctions,  though  some  are  more  important  than 
others. 

About  midsummer  the  progress  of  vegetation  seems  to  be 
suspended,  and  for  several  days  the  vital  energies  of  the  tree 
are  exerted  in  the  formation  of  buds.  We  no  longer  observe 
the  vigorous  growth  of  spring,  but  if  we  examine  the  young 
branches,  we  shall  find  the  newly  formed  buds  at  the  base 
of  the  leaf-stalk,  immediately  above  the  place  of  their  inser- 
tion. After  the  fall  of  the  leaves  they  are  more  conspicuous, 
and  during  the  winter  we  may  perceive  a  gradual  enlarge- 
ment, corresponding  to  the  developement  of  the  tender  germs 
which  they  enclose.  Plants,  as  is  well  known,  may  be  pro- 
pagated by  buds,  and  in  that  sense  each  bud  is  a  separate 
being,  or  a  young  plant  in  itself;  but  such  propagation  is  only 
the  extension  of  an  individual,  and  not  a  rc-production  of  the 
species,  as  by  seed. 

Leaves  are  eminently  ornamental  to  plants  from  their  pleaa* 
ing  colour,  and  the  infinite  variety  as  well  as  elegance  of 
their  forms.  Their  different  situations,  insertions,  forms, 
and  surfaces,  which  are  of  the  greatest  possible  use  in  sys- 
tematical botany,  cannot  here  be  described.  A  knowledge 
of  their  real  use  with  regard  to  the  plant  is  a  curious  branch 
of  vegetable  physiology.  That  leaves  give  out  moisture,  or 
are  organs  of  insensible  perspiration,  is  proved  by  the  simple 
experiment  of  gathering  the  leafy  branch  of  a  tree,  and  im- 
mediately stopping  the  wound  at  its  base  with  wax  to  pre- 
vent the  effusion  of  moisture  in  that  direction.  In  a  very 
short  time  the  leaves  droop,  wither,  and  are  dried  up.  If  the 
same  branch,  partly  faded,  though  not  dead,  be  placed  in  a 
very  damp  cellar,  or  immersed  in  water,  the  leaves  revive, 
by  which  their  power  of  absorption  is  also  proved.  A  know^- 
ledge  of  the  perspiring  and  absorbing  power  of  leaves  is  often 
of  great  practical  importance.  It  teaches  us  that  plants 
droop,  in  consequence  of  the  excess  of  the  former,  and  are 


|tt. 


•204  LEAVES.  ^ 

to  be  revived  by  diminishing  their  discharge,  or  increasing  ; 

their  absorption.     The  former  is  accompHshed  by  confining  j 

the  air  around  them,  and  the  latter  by  sprinkling  water  over  \ 

the  leaves  ;  and  when   plants  have  recently  been  removed,  j 

audi  management  is  frequently  required,  ' 

Air  is  not  less  essential  to  the  healthy  existence  of  ani-  j 

mals  than  of  plants.     One  great  use  of  leaves  is  to  perform,  ] 

in  some  measure,  the  same  office  for  the  support  of  vegeta-  = 

ble  life,  that  the  lungs  of  animals  do  for  the  support  of  ani-  , 

mal  life.     Light  has  a  very  powerful  effect  upon  plants,  and  1 

the  green  colour  of  leaves  is  so  much  owing  to  it,  that  plants  j 

raised  in  darkness  are  of  a  sickly  white      Light  acts  bene-  \ 

ficially  upon  the  upper  surface  of  leaves,  and  hurtfully  upon  ] 

the  under  side  ;  hence  the  former  is  always  turned  towards  j 

the  light,  in  whatever  situation  the  plant  may  be  placed.     A  ] 

great  number  of  leaves  follow  the  sun  in  its  course,  and  a  4 

familiar  instance  of  this  is  a  clover-field.     The  leaves  of  some  | 

plants,  when  the  light  is  withdrawn,  fold  over  each  other,  or  ^ 

droop  as  if  dying  ;  and  this  is  called  by  Linnseus  the  sleep  I 

of  plants.     Some   leaves  display  an  extraordinary  sensibi-  ; 

lity  to  the  touch  of  any  extraneous  body,  or  to  any  sudden  J 

concussion,  as  those  of  the  sensitive  plant.     An  impression  < 

made,  in  the  most  gentle  manner,  upon  one  of  its  leaflets,  is  ] 

communicated  in  succession  to  all  of  them,  evincing  an  ex-  I 

quisite  irritability.     The  moving  plant  of  India  exhibits  such  ' 
powers  as  to  excite  the  astonishment  of  every  beholder.     If 

its  motion   be  impeded,   no  sooner  does  it  regain  its  liberty  j 

than  its  operations  are  renewed  with  increased  activity,  as  if  ' 

it  were  necessary  to  redeem  the  time  which  it  had  lost.     Its  | 

winged  leaves  seem  to  disdain  to  rest,  and  to  exhibit  a  most  ■ 

astonishing  example  of  industry.  \ 

Questions. — 1.  What  are  the  two  parts  of  the  root  of  a  plant  ?  2.    i 
How  are  roots  divided  with    regard  to  their  duration  ?    3.  Give  the    ') 
examples.    4.  What  is  said  of  buds  ?    5.  How  is  it  proved  that  leaves    | 
are   organs   of  perspiration,   and  of  absorption  ?    6.  What  office  do    \ 
leaves  perform  for  plants  ?    7.  What  is  the  effect  of  light  upon  plants,    j 
and   leaves  ?    8.  What  is    said  of  the    sensitive  plant  ?    9.  Of  the    ; 
moving   plant  of  India  ?    10.  Describe  tho  several  kinds  of  Roots,    i 
(see  Appendix.)    11.  What  is  said  of  the  root  of  common  herds  grass  ? 
12.  What  are  the  seven  kinds  of  trunks  or  stems  .•*    13.  What  are  the 
several  kinds  of  appendages  to  a  plant .''    14.  What  are  the  several 
kinds  of  Inflorescence  ? 


FLOWER  AND  FRUIT.  205 


LESSON  92. 


Flower  and  Fruit. 

Fil'iform,  thread  like,  or  very  slender. 

Ves'icle,  a  small  cuticle,  filled  or  inflated,  or  a  little  bladder. 

Go,  mark  the  matchless  working  of  the  Power 
That  shuts  within  the  seed  the  future  flower ; 
Bids  these  in  elegance  of  form  excel, 
In  colour  these,  and  those  delight  the  smell ; 
Sends  nature  forth,  the  daughter  of  the  skies, 
To  dance  on  earth,  and  charm  all  human  eyes. 

COWPER. 

LiNN^us  classed  the  flower  and  fruit  together,  and  defined 
them  to  be  a  temporary  part  of  vegetables,  destined  for  the 
reproduction  of  the  species,  terminating  the  old  individual 
and  beginning  the  new.  These  constitute  the  reproduc- 
tive organs,  by  which  the  species  have  been  hitherto  pre- 
served from  extinction,  and  by  which  alone  they  will  be  re- 
newed, so  long  as  seed  time  and  harvest  continue.  There 
are  seven  of  these  organs,  some  of  which  are  essential  to  the 
very  nature  of  flower  or  fruit,  others  not  so  indispensably 
necessary,  and  therefore  not  universal.  The  student,  who 
wishes  to  gain  an  adequate  idea  of  these  organs,  should  dis- 
sect diff*erent  flowers,  and  bestow  upon  each  part  a  separate 
examination.  He  will  find  externally  the  cal'yx  or  flower- 
cup,  usually  of  a  green  colour,  and  often  wanting;  the 
corol'la,  or  as  it  is  sometimes  termed  the  blossom,  assuming 
various  shades  of  colour,  exhibiting  a  more  delicate  texture 
than  the  preceding,  and  like  it  sometimes  wanting ;  the 
stamens,  which  are  filiform  organs  arranged  interior  to  the 
corolla,  and  are  never  wanting;  i\\e pistils,  arising  from  the 
centre  of  the  flower,  containing  the  rudiments  of  the  fruit, 
and  of  course  essential ;  the  seed-vessel,  of  a  pulpy,  woody, 
or  leathery  texture,  enclosing  the  seeds,  but  wanting  in  many 
plants  ;  the  scad,  the  perfecting  of  which  is  the  sole  end  of 
all  the  other  parts ;  and  the  receptacle,  or  base,  which  is  the 
point  oficonnexion,  and  must  necessarily  be  present  in  some 
form  or  other. 

The  corolla  constitutes  the  chief  beauty  of  a  flower,  and 
includes  two  parts,  the  Petal  and  the  Nectary.  The  former 
18 


206  FLOWER  AND  FRUIT. 

is  either  simple,  as  in  the  primrose  and  bell  shaped  flowers, 
in  which  case  the  corolla  is  said  to  be  monopet'alous ;  or 
compound,  as  in  the  rose,  in  which  it  is  polypet'alous.  The 
whole  use  and  physiology  of  the  corolla  have  not  yet  been 
fully  explained.  The  nectary  contains  or  secretes  honey  ; 
and  there  can  be  no  doubt  that  the  sole  use  of  the  honey  with 
respect  to  the  plant  is  to  tempt  insects,  who  in  procuring  it 
fertilize  the  flower,  by  disturbing  the  dust  of  the  stamens, 
and  even  carry  that  substance  from  the  barren  to  the  fertile 
blossoms.  A  stamen  commonly  consists  of  two  parts,  the 
Filament  and  Anther,  the  former  being  merely  what  sup- 
ports the  latter,  which  is  the  only  essential  part.  The  an- 
ther is  generally  of  a  membranous  texture,  consisting  of  two 
cells  or  cavities.  It  contains  the  Pollen,  or  Dust,  which  is 
thrown  out  chiefly  in  warm  dry  weather,  when  the  coat  of 
the  anther  contracts  and  bursts.  The  Pollen,  though  to 
the  naked  eye  a  fme  powder,,  and  light  enough  to  be  wafted 
along  by  the  air,  is  so  curiously  formed,  and  so  various  in 
different  plants,  as  to  be  an  interesting  and  popular  object 
for  the  microscope.  Each  grain  of  it  is  a  round  or  angular, 
rough  or  smooth  vesicle,  which  remains  entire  till  it  meets 
with  any  moisture,  being  contrary  in  this  respect  to  the  na- 
ture of  the  anther  ;  then  it  bursts  with  great  force,  discharg- 
ing a  most  subtile  vapour. 

The  Pistil  consists  of  three  parts  :  the  Germen,  or  rudi- 
ment of  the  young  fruit  and  seed  ;  the  style,  various  in  If-igth 
and  thickness,  sometimes  altogether  wanting,  and  when 
present  serving  merely  to  elevate  the  third  part,  which  is 
called  the  Stigma.  This  last  is  indispensable.  It  is  very 
generally  downy,  and  always  more  or  less  moist.  The 
moisture  is  designed  for  the  reception  of  the  pollen,  which 
explodes  on  meeting  with  it,  and  hence  the  seeds  are  fertilized 
and  rendered  capable  of  ripening,  which  they  would  not 
otherwise  be,  though  in  many  plants  fully  formed. 

The  ways  in  which  insects  serve  the  purpose  of  perfecting 
the  seeds  in  plants  are  innumerable.  These  active  little 
beings  are  peculiarly  busy  about  flowers  in  bright  sunny 
vveatherj  when  every  blossom  is  expanded,  the  pollen  in  per- 
fection, and  all  the  powers  of  vegetation  in  their  greatest 
vigour.  Then  we  see  the  rough  sides  and  legs  of  the  bee, 
laden  with  the  golden  dust  which  it  shakes  off,  and  collects 
anew,  in  its  visits  to  the  honeyed  stores  inviting  it  on  every 


CLASSIFICATION  OF  VEGETABLES.  20t 

side.  All  nature  is  then  alive,  and  a  thousand  wise  ends 
are  then  accomplished  by  innumerable  means  that  "  seeing 
we  perceive  not;"  for  tliough  in  the  abundance  of  the  crea- 
tion there  seems  to  be  a  waste,  yet  in  proportion  as  we  un- 
derstand the  subject,  we  find  the  more  reason  to  conclude 
that  nothing  is  made  in  vain. 

Questions.  1.  How  did  Linnaeus  define  "the  fiower  and  fruit  ?  2. 
What  do  these  constitute  ?  3.  What  is  said  of  the  number  and  im- 
portance of  these  organs  ?  4.  Describe  the  several  parts  belonging  to 
the  flower  and  fruit.  5.  What  two  parts  does  the  corolla  include  ?  6. 
When  is  the  corolla  termed  monopetalous  ?  7.  Polypetalous  ?  8. 
What  is  the  use  of  the  honey  with  regard  to  the  plant  ?  9.  What  are 
the  parts  of  a  stamen  termed?  10.  Describe  the  anther.  11.  The 
Pollen.  12.  What  are  the  parts  of  the  Pistil .?  13.  Describe  the  stig- 
ma. 14.  What  are  the  seven  kinds  into  which  the  calyx  is  divided  ? 
(see  Appendix)  15.  What  are  the  seven  kinds  of  seed  vessels  ?  16. 
What  are  some  of  the  parts  of  which  the  seed  itself  is  composed  .-*  17. 
Look  at  Engr.  VII.  and  describe  the  parts  of  the  flower  and  fruit  of  the 
Lily,  (see  the  description  in  Appendix  to  Lesson  93.) 


LESSON  93. 

Classification  of  Vegetables. 

Ge'nus,  (plural  gen^'era)  a  set  of  plants,  animals,  or  other  things, 

comprehending  many  species. 
Nomencla'ture,  a  term  employed  to  denote  the  language  peculiar 

to  any  particular  science  or  art :  a  vocabulary. 

All  the  known  vegetable  productions,  upon  the  surface 
of  the  globe,  have  been  reduced  by  naturalists  to  Classes, 
Orders,  Genera,  Species,  and  Varieties.  The  classes  are 
composed  of  orders ;  the  orders  of  genera  ;  the  genera  of 
species ;  and  the  species  of  varieties.  We  may  attain  a 
clearer  idea  of  them,  by  comparing  them  with  the  general 
divisions  of  the  inhabitants  of  the  earth.  Vegetables  resem- 
ble Man ;  Classes,  nations  of  men  ;  Orders,  tribes,  or 
divisions  of  nations  ;  Genera,  the  families  that  compose 
the  tribes ;  Species,  individuals  of  which  families  consist ; 
and  Varieties,  individuals  under  different  appearances. 

Linnaeus,  dissatisfied  with  every  system  invented  before  his 
time,  undertook  to  form  a  new  one.  With  an  eye  which  could 
at  a  single  glance  discern  the  peculiar  features  of  an  object ; 
with  firmness  to  encounter,  and  with  talents  to  overcome, 


208 


CLASSIFICATION 


the  greatest  difficulties,  he  planned  and  accomplished  more 
than  all  his  predecessors,  and  his  works  which  remain  at  this 
day  unrivalled,  will  probably  long  continue  unequalled.  The 
number,  situation,  and  proportion  of  the  stamens  v/ere  the 
foundation  of  his  primary  divisions.  These  organs,  so  con- 
stant, so  essential  to  the  completion  of  the  flower,  so  neces- 
sary for  the  preservation  of  the  vegetable  kingdom,  were 
happily  selected  to  furnish  each  of  his  Classes  with  an  obr 
vious  inmiutable  character.  The  Orders  into  which  his 
classes  are  subdivided,  are  established  on  a  basis  equally 
constant,  on  the  number  and  situation  of  the  pistils,  or  on 
some  other  circumstance  equally  obvious  and  invariable.  A 
Genus  is  a  subdivision  of  an  order,  and  includes  such  plants 
as  agree  with  each  other  in  the  form  and  situation  of  their 
flowers  and  fruits.  A  Species  consists  of  such  as  agree 
in  these  particulars,  but  differ  in  the  form  of  their  root,  stem, 
leaves,  and  other  parts. 

A  remark,  which  has  sometimes  been  made  to  the  preju- 
dice of  the  study  of  Botany,  is,  that  it  is  a  mere  nomencla- 
ture, tending  only  to  burden  the  memory  with  an  immense 
list  of  names,  without  imparting  to  the  student  any  degree 
of  real  and  useful  knowledge.  But  is  it  a  small  gratifica- 
tion, or  of  small  importance,  to  be  enabled  to  distinguish, 
at  first  sight,  the  productions  of  the  vegetable  kingdom,  and 
to  refer  them  to  their  proper  classes,  families,  and  stations? 
The  disadvantages  resulting  from  the  neglect  of  this  study, 
are  seldom  more  seriously  felt  than  in  the  perusal  of  those 
narratives  of  voyages  and  travels,  which  are  now  so  profuse- 
ly published.  In  passing  through  countries  which  have 
seldom  been  visited,  it  is  in  the  highest  degree  desirable, 
that  the  adventurer  should  be  able  to  avail  himself  of  the 
opportunities  afforded  him,  so  as  to  render  his  labours  of 
substantial  service  to  mankind  :  but  how  is  this  to  be  effected, 
unless  he  be  previously  furnished  with  suflficient  knowledge 
to  distinguish  those  natural  productions  which  it  may  be 
thought  important  either  to  procure  or  describe  1  For  want 
of  this  knowledge,  which  v/ould  enable  him  to  acquaint  us 
in  two  words  with  the  name  of  any  known  plant,  and  to  re- 
fer to  its  proper  station  every  one  which  is  unknown,  we  have 
endless  descriptions  of  unknown  and  surprising  vegetables, 
which  either  give  us  no  precise  idea,  or  by  a  long  and  cir- 
cuitous track,  enable  us  at  length  to  recognise  an  old  and 


OF  VEGETABLES. 


209 


familiar  acquaintance.  A  striking  instance  of  this  may  be 
found  in  the  celebrated  Kotzebue's  narrative  of  his  banish- 
ment to  Siberia,  in  the  course  of  which  he  discovered  a 
plant  vv'hich  attracted  in  a  high  degree  his  admiration,  and 
which  he  has  described  at  great  length,  as  one  of  the  most 
beautiful  flowers  he  had  ever  met  with.  A  very  moderate 
acquaintance  with  botanical  science  would  however  have  in- 
formed him,  that  this  plant  was  already  known  to  most  parts 
of  Europe ;  and  the  only  doubt  which  remains  is,  as  to  the 
particular  species  of  the  plant,  a  doubt  which  his  description 
does  not  after  all  enable  us  to  clear  up. 

The  natural  history  of  animals,  though  in  many  respects 
more  interesting  than  botany  to  man  as  an  animated  being, 
and  more  striking  in  some  of  the  phenomena  which  it  dis- 
plays, yet,  in  other  points,  is  less  pleasing  to  a  tender  and 
delicate  mind.  In  botany  all  is  elegance  and  delight.  No 
painful  experiments  are  to  be  made.  Its  pleasures  spring  up 
under  our  feet,  and,  as  we  pursue  them,  reward  us  with 
health  and  setene  satisfaction.  None  but  the  most  foolish 
or  depraved  could  derive  any  thing  from  it  but  what  is  beau 
tiful,  or  pollute  its  lovely  scenery  with  unamiable  or  unhal- 
lowed images.  Those  who  do  so,  either  from  corrupt  taste 
or  malicious  design,  can  be  compared  only  to  the  fiend  en- 
tering into  the  garden  of  Eden. 

Questions. — 1.  How  have  naturalists  arranged  vegetables?  2. 
Give  the  illustration.  3.  What  are  the  foundations  of  the  Linnasan 
Classes  i* — Orders  ?  4.  What  does  a  genus  include  .''  5.  A  Species  ? 
6.  What  remark  has  been  made  to  the  prejudice  of  the  study  of  bota- 
ny .''  7.  What  is  said  to  obviate  this  objection  .''  8.  What  is  related 
of  Kotzebue  .''  9.  What  is  said  of  botany  as  compared  with  the  natural 
history  of  animals .''  10.  What  are  the  names  of  the  twenty-four 
classes  .-*  11.  Of  the  orders  of  the  first  thirteen  classes  ?  12.  Give  an 
example  of  the  divisions  of  classes,  orders,  &c.  13.  How  is  the  spe- 
cies of  a  plant  distinguished  ?  (For  answers  to  the  four  last  questions, 
see  Appendix.)  14.  Look  at  Engr.  VH.  and  describe  the  parts  of  the 
flower  and  fruit  of  the  geranium. 
18* 


910 


FLOWERS 


m 


LESSON  94. 


Flowers. 


Carnation,  a  fine  and  fragrant  flower  whose  varieties  of  colour 
and  luxuriance  are  innumerable.  Class  Decandria,  order 
Digynia,  genus  Dianthus. 

The  infinite  variety  of  flowers  is  not  less  a  subject  of  ad- 
miration than  their  regular  succession,  and  equally  evinces 

*  4r  consummate  wisdom  and  design.  This  diversity  is  not  dis- 
cernible only  in  the  different  families  of  flowers,  but  it  is  to 
be  seen  in  the  individuals.  In  a  bed  of  tulips  or  carnations, 
there  is  scycely  a  flower  m  which  some  difference  may  not 

^  be  observed  in  its  structure,  size,  or  assemblage  of  colours ; 
nor  can  any  two  flowers  be  found  in  which  the  shape  and 
shades  are  exactly  similar.  Flowers  have  not  only  furnished 
the  poets  with  inexhaustible  description,  but  the  philoso- 
j»hers  in  every  age  with  a  variety  of  moral  sentiments.  Those 
who  have  gathered  a  rose,  know  but  too  well  how  soon  it 
withers ;  and  the  familiar  application  of  its  fate  to  that  of 
human  life  and  beauty  is  not  more  striking  to  the  imagina- 
tion than  philosophically  and  literally  true. 

The  following  interesting  account  has  been  given  by  Sir 
John  Hill  of  what  appeared  on  examining  a  carnation.  Its 
fragrance  led  me  to  enjoy  it  frequently  and  near ;  the  sense 
of  smelling  was  not  the  only  one  affected  on  these  occasions ; 
while  that  was  satisfied  with  the  })owerful  sweet,  the  ear  was 
constantly  attacked  by  an  extremely  soft  but  agreeable  mur- 
muring sound.  It  was  easy  to  know  that  some  animal 
within  the  covert,  must  be  the  musician,  and  that  the  little 
noise  must  come  from  some  little  creature  suited  to  produce 
it.  I  instantly  distended  the  lower  part  of  the  flower,  and 
placing  it  in  a  full  light,  could  discover  troops  of  little  in- 
sects frisking  with  wild  jollity  among  the  narrow  pedestal 
that  supported  its  leaves,  and  the  little  threads  that  occupied 
its  centre.  What  a  fragrant  world  for  their  habitation  I 
What  a  perfect  security  from  all  annoyance,  in  the  dusky 
husk  that  surrounded  the  scene  of  action  !  Adapting  a  mi- 
croscope to  take  in  at  one  view  the  whole  base  of  the  flower,  I 
gave  myself  an  opportunity  of  contemplating  what  they  were 
»bout,  and  this  for  many  days  together,  without  giving  them 


FLOWERS.  211 

the  least  disturbance.  Thus  I  could  discover  their  economy, 
their  passions,  and  their  enjoyments.  The  microscope  had 
given,  on  this  occasion,  what  nature  seemed  to  have  denied 
to  the  objects  of  contemplation.  The  base  of  the  flower  ex- 
tended itself  under  its  influence  to  a  vast  plain  ;  the  slender 
stems  of  the  leaves  became  trunks  of  so  many  stately  cedars  ; 
the  threads  in  the  middle  seemed  columns  of  massy  structure, 
supporting  at  the  top  their  several  ornaments  ;  and  the  nar- 
row spaces  between  were  enlarged  in  walks,  parterres,  and 
terraces.  On  the  polished  bottoms  of  these,  brighter  than 
Parian  marble,  walked  in  pairs,  alone,  or  in  larger  companies, 
the  winged  inhabitants;  these, from  little  dusky  flies,  for 
such  only  the  naked  eye  would  have  shown  them,  were 
raised  to  glorious  glittering  animuls,  stained  with  living  pur- 
ple, and  with  a  glossy  gold  that  would  have  made  all  the 
labours  of  the  loom  contemptible  in  the  comparison.  I 
could  at  leisure,  as  they  walked  together,  admire  their  ele- 
gant limbs,  their  velvet  shoulders,  and  their  silken  wings  ; 
their  backs  vieing  with  the  empyrean  in  its  blue  ;  and  their 
eyes  each  formed  of  a  thousand  others,  out-glittering  the 
little  planes  on  a  brilliant :  above  description,  and  too  great 
almost  for  admiration.  I  could  observe  them  here  singling 
out  their  mates,  entertaining  them  with  the  music  of  their 
buzzing  wings,  with  little  songs  formed  for  their  little  or- 
gans, leading  them  from  walk  to  walk  among  the  perfumed 
shades,  and  pointing  out  to  their  taste  the  drop  of  liquid  nec- 
tar just  bursting  from  some  vein  within  the  living  trunk  ; 
here  were  the  perfumed  groves,  the  more  than  myrtle  shades 
of  the  poet's  fancy  realized.  Here  in  the  triumph  of  their 
little  hearts,  they  skipped  from  stem  to  stem  among  the 
painted  trees  ;  or  winged  their  short  flight  to  the  close 
shadow  of  some  broader  leaf — 

"  All  formed  with  proper  faculties  to  share 
The  daily  bounties  of  their  Maker's  care." 

NoTB.  The  night-flowering  cereus  (cactus  grandiflorvs)  is  one  of 
our  most  splendid  hot-house  plants,  and  is  a  native  of  Jamaica  and 
some  other  of  the  West  India  Islands.  Its  stem  is  creeping,  and 
thickly  set  with  spines.  The  flower  is  white  and  very  large,  some- 
times nearly  a  foot  in  diameter.  The  most  remarkable  circumstance 
with  regard  to  the  flower  is  the  short  time  it  lakes  to  expand,  and 
the  rapidity  with  which  it  decays.  It  begins  to  open  late  in  the  even 
ing,  flourishes  for  an  hour  or  two,  then  begins  to  droop,  and  befort 
morning  u  completely  dead. 


212  ANIMAL    KINGDOM. 


LESSON  95. 

Animal  Kingdom. 

Zo-o\'ogy,  that  branch  of  natural  history  which  treats  of  animals. 
Ver'tebre,  (pronounced  ver'te-bur,)  a  joint  of  tne  spine. 

Few  departments  of  knowledge  are  more  interesting  than 
the  natural  history  of  animals,  and  the  attention  given  to  it 
in  the  present  age  furnishes  the  best  evidence  that  its  claims 
to  notice  begin  to  be  fully  estimated.  In  our  own  country  the 
inducements  to  its  cultivation  are  peculiarly  strong,  for  our 
immense  lakes,  forests,  and  mountains,  have  as  yet  been  but 
imperfectly  explored  by  naturalists,  and  the  little  that  is 
known  of  their  productions  leads  to  the  belief,  that  they  con- 
tain abundance  to  encourage  and  reward  the  labours  of 
science. 

The  study  of  Zoology  is  particularly  advantageous  to  the 
young,  from  its  direct  tendency  to  cultivate  one  of  the  most 
useful  habits  of  the  mind,  that  of  attentive  observation  of 
things  of  common  and  daily  occurrence.  Its  objects  are 
every  where  around  us, — swimming  in  the  waters,  flying  in 
the  aiif-,  walking  the  earth,  and  burrowing  beneath  it.  One 
set  provides  our  food  and  clothing,  another  purloins  and  de- 
stroys them.  Some  attack,  and  others  protect  us.  Their 
forms  are  continually  before  our  eyes,  and  their  voices  always 
sounding  in  our  ears. 

In  order  to  treat  clearly  of  the  animal  kingdom,  it  is  ne 
cessary  to  consider  it  according  to  some  method  of  arrange- 
ment, by  which  those  apimals  which  most  resemble  one  ano- 
ther are  connected  together  for  the  convenience  of  descrip- 
tion. This  arrangement  is  founded  upon  their  form  and 
structure,  and  separates  them  into  various  divisions  and  sub- 
divisions, according  to  their  degree  of  similarity,  and  the 
points  in  which  their  structures  correspond.  Such  a  system 
of  arrangement  is  called  a  classification  of  the  animal  king- 
dom ;  and  an  accurate  acquaintance  with  the  principles  on 
which  it  is  founded  will  be  of  great  assistance  to  the  student 
of  natural  history. 

All  animals  are  divided  in  the  first  place  into  two  grand 
divisions,  namely,  into  vertebral,  embracing  those  that  have 
a  spine,  otvertebres,  and  into  invertebral,  comprehending  all 


FIRST  CLASS  OF  ANIMALS.  213 

those  that  are  destitute  of  a  spine,  or  vertebral  column.  The 
vertebral  animals  are  subdivided  into  four  classes,  and  the 
invertebral  into  five.  {See  Appendix.)  Each  of  the  classes  is 
divided  into  a  greater  or  less  number  of  orders,  distinguish- 
ed by  some  important,  clear,  and  remarkable  peculiarities 
of  conformation  and  structure,  which  are  common  to  all  the 
animals  included  under  each  of  them.  Orders  arc  subdivid- 
ed into  genera.  These  comprehend  animals  that  have  a  ge- 
neral external  resemblance  to  each  other,  a  kind  of  family 
likeness.  Genera  are  made  up  of  species.  Each  distinct 
kind  of  animal  constitutes  a  species,  and  they  are  known 
from  one  another  by  their  size,  colour,  form,  and  various 
other  circumstances  of  external  appearance. 

Each  kind  of  animal,  then,  constitutes  a  distinct  .spcc/e5 ;  a 
number  of  species  taken  together  form  a  genus ;  those  ge- 
nera which  have  important  and  well  defined  points  of  resem- 
blance in  structure  and  conformation  common  to  all,  are 
placed  together  in  an  order  ;  whilst  upon  a  similar  principle, 
but  more  extensive  in  its  application,  these  orders  are  mar- 
shalled into  separate  classes. 

Questions — 1.  What  are  theinducesncnts  to  the  study  of  Zoolo- 
gy in  our  own  country  ?  2.  Why  is  this  study  advantageous  to  the 
young?  3.  Upon  what  is  a  classification  of  the  onimal  kingdom 
founded  ?  4.  VVhat  are  the  first  twq  grand  divisions  ?  5.  How  are 
these  subdivided  ?  G.  What  arc  classes  ?  7.  Orders  ?  8.  Genera?  9. 
Species?  10.  Give  a  general  definition  of  species,  genus,  order,  and 
class.  11.  What  are  the  nine  classes  of  the  animal  kingdom  ?  12.  How 
many  and  what  are  the  classes  according  to  Linnaeus  ?  [Note.  In  the 
exercise  of  reading,  the  words  included  in  parentheses  and  italicized 
should  be  passed  over.  They  are  placed  in  the  lessons  that  the  atten- 
tion of  pupils  may  be  particularly  directed  to  them.  Pupils  should 
mention  them  in  answering  the  questions.] 


LESSON  96. 

The  first  Class  of  Animals  {Mammalia.) 

The  animals  of  this  class  are  distinguished  for  a  more 
perfect  bodily  structure,  for  more  varied  faculties,  more  de- 
licate sensations,  a  more  elevated  intelligence,  and  greater 
capability  of  improvement  by  imitation  and  education,  than 
those  of  any  other.     It  is  to  this  class  that  man,  considered 


^        214  MAN. 

as  an  object  of  natural  history,  properly  belongs.  He  is  af- 
ranged  with  the  animals  of  this  class,  because  he  nearly  re- 
sembles them  in  structure  and  organs,  though  raised  in  reality 
far  above  them  by  the"  possession  of  intellectual  and  moral 
powers  almost  infinitely  superior. 

The  structure  of  an  animal  is  always  found  to  correspond 
to  its  character,  mode  of  life,  and  food ;  and  those,  there- 
fore, which  have  a  similar  structure,  resemble  one  another 
to  the  same  extent  in  other  particulars.  From  the  formation 
of  the  anterior  extremities  of  an  animal,  we  may  judge  of  the 
degree  of  address  of  which  he  is  capable,  and  of  the  kind 
of  motions  he  is  able  to  perform  ;  and  from  the  structure  of 
his  teeth,  what  is  the  nature  of  his  food.  Thus,  the  fore-feet 
^  of  animals  may  be  either  enveloped  in  hoofs,  or  armed  with 
claws,  or  furnished  with  slender  nails  ;  and  the  perfection 
of  the  sense  of  touch  will  be  in  proportion  to  the  delicacy 
of  these  organs  respectively.  Thus  too,  there  are  three 
kinds  of  teeth  ;  the  incisive  or  cutting  teeth,  the  canine  or 
lacerating  teeth,  and  the  molar  or  grinding  teeth ;  but  all 
animals  have  not  each  of  these  kinds  of  teeth,  nor  are  they 
of  the  same  shape  and  formation  in  all  animals. 

It  is  principally  from  a  regard  to  these  parts,  that  natural- 
ists have  proceeded  in  the  arrangement  of  this  class  of  ani- 
mals. The  orders  thus  formed  are  nine  in  number.  {Sec 
Appendix.)  Of  the  first  order  {Biman'a)  man  is  the  only 
example.  In  point  of  adroitness,  skill,  and  address,  the 
structure  of  his  body  and  the  faculties  of  his  mind  give  him 
great  advantages  over  other  animals.  In  consequence  of  his 
erect  position,  he  has  the  free  use  of  his  hands,  and  his  arms 
have  unincumbered  and  various  motions  in  every  direction. 
There  are  several  distinct  races  of  mankind  inhabiting  diffe- 
rent portions  of  the  earth,  which  differ  one  from  another 
more  or  less  in  form,  in  features,  in  complexion,  and  in  cha- 
racter. The  cause  of  these  varieties  has  never  been  satis- 
factorily pointed  out.  They  have  been  attributed  to  climate, 
to  situation,  and  to  manner  of  life,  but  none  of  these  circum- 
stances appear  sufficient  to  produce  them,  and  we  therefore 
still  remain  in  ignorance  on  the  subject.  But  notwithstand- 
ing the  differences  in  man,  he  maintains  every  where  a  de- 
cided rank,  far  above  that  of  any  other  animal.  He  is  the 
only  one  which  has  the  power  of  communicating  its  thoughts 
and  feelings  by  articulate  speech ;  the  only  one  which  can 


ORDERS    OP    MAMMALIA.  215 

properly  be  said  to  avail  itself  of  the  advantages  of  society  ; 
and  the  only  one  that,  strictly  speaking  educates  its  young. 
It  is  in  consequence  of  these  advantages,  particularly  that 
derived  from  association,  that  he  has  been  enabled  under  all 
circumstances,  to  acquire  and  preserve  a  dominion  over 
other  animals,  to  protect  himself  against  the  severity  of  cli- 
mates, and  thus  spread  his  species  over  every  part  of  the 
earth.  Naturally  tender  and  defenceless,  he  could  only  ex- 
ist in  the  most  equable  and  temperate  climates  ;  but,  aided 
by  the  inventions  and  discoveries  of  social  life,  he  is  enabled 
to  brave  the  cold  of  the  polar  circle,  as  well  as  the  overpow- 
ering heat  of  the  regions  on  the  equator. 

The  second  order  {Quadruman' a,  apes,  baboons,  S^c.)  of 
this  class  of  animals  forms  a  numerous  tribe,  and  compre- 
hends a  great  variety  of  species.  They  maintain  the  erect 
position  with  difficulty ;  it  is  a  constrained  one.  Their 
structure  evidently  fits  them  for  climbing,  and  their  usual 
places  of  habitation  are  trees,  on  the  fruits  of  which  they 
feed. 

The  third  order  is  subdivided  into  several  tribes  or  fami- 
lies, accordingly  as  they  are  more  or  less  carnivorous.  The 
first  tribe  is  that  of  the  Bats,  distinguished  by  their  wings, 
which  are  formed  of  a  thin  fold  of  skin,  extending  between 
the  two  limbs  of  the  same  side.  By  means  of  this  apparatus, 
many  of  them  are  able  to  fly  with  a  force  and  rapidity  equal 
to  that  of  birds  ;  but  in  others  it  answers  only  the  purpose 
of  a  parachute  to  break  their  fall  from  lofty  places,  or  to  ena- 
ble them  to  perform  great  leaps  in  their  passage  from  tree  to 
tree.  The  second  tribe  includes  a  number  of  small  animals, 
which  feed  principally  upon  insects,  and  are  called  insec- 
tiv'orous,  as  the  shrew-mouse  and  the  mole.  The  third  tribe 
possesses  the  characteristics  of  carnivorous  animals  in  the 
highest  degree.  They  are  endowed  not  only  with  an  appe- 
tite for  animal  food  and  a  structure  adapted  for  its  mastica- 
tion and  digestion,  but  with  strength  and  courage  for  seizing 
and  retaining  it ;  as  the  wolf,  fox,  lion,  panther,  and  others. 
A  fourth  tribe  of  this  order  comprehends  the  amphibious 
animals,  as  the  Seal  and  the  Morse.  They  live  almost  en- 
tirely in  the  sea,  but  they  cannot  remain  constantly  under 
water. 

The  fourth  order  (Rodcn'tia,  gnawers)  are  remarkably 
qualified  by  the  arrangement  of  their  teeth  for  penetrating 


210  ORDERS    OF    MAMMALIA* 

very  solid  substances ;  and  they  frequently  feed  u}K)n  woody 
fibres  and  the  bark  of  roots  and  trees.  Of  this  order,  among 
others,  are  the  beaver,  the  squirrel,  and  the  various  species 
of  hare  and  rabbit.  Beavers  are  aquatic  animals,  and  they 
construct  themselves  habitations  upon  waters  which  are  suf- 
ficiently deep  never  to  be  frozen  to  the  bottom. 

The  fifth  order  {Eclenta'ta,  toothless)  are  remarkable  for 
a  great  degree  of  torpor,  listlessness,  and  indisposition  to 
motion  ;  but  some  more  than  others.  The  sloth,  the  ant- 
cater,  and  the  armadillo  are  among  them,  and  of  each  of 
tlrese  there  are  several  species.  The  three-toed  sloth  is  an 
animal  whose  very  aspect  is  painful  and  disgusting.  The 
expression  of  its  countenance,  and  its  whole  attitude,  indeed, 
convey  to  the  beholder  the  impression,  that  its  very  existence 
is  a  burden. 

Ruminating  animals  form  the  sixth  order  of  this  class,  and 
examples  may  be  found  in  the  camel,  antelope,  deer,  ox,  and 
sheep.  They  have  been  more  valuable  to  man  than  any 
others.  Their  flesh  furnishes  a  large  proportion  of  our  ani- 
mal food.     They  are  mild,  docile,  and  easily  domesticated. 

The  seventh  order  {Pachyder'mata,  thick-skinned)  em- 
braces ail  the  animals  w  ith  hoofs  which  do  not  ruminate,  as 
the  elephant,  the  tapir,  the  horse.  The  Hippopot'amus,  or 
River-Horse,  inhabits  principally  the  rivers  of  the  south  of 
Africa.  It  walks  with  ease  at  the  bottom  of  the  water,  though 
obliged,  occcasionally,  to  rise  to  the  surface  for  breath. 

Animals  of  the  whale  kind,  or  cetaceous  animals,  form  the 
eighth  order.  They  are  usually  confounded  with  the  class 
of  fishes,  which  they  resemble  in  many  particulars  of  exter- 
nal appearance,  as  well  as  in  the  circumstance  of  residing 
always  in  the  water.  In  point  of  structure,  however,  they 
clearly  belong  to  the  present  class,  since  they  breathe  air  by 
means  of  lungs,  are  warm-blooded,  produce  their  young  alive, 
and  nourish  them  with  milk. 

The  Marsii' pial  animals,  which  form  the  ninth  order,  are 
distinguished  from  all  others  by  the  possession  of  a  recep- 
tacle, formed  by  a  duplicature  of  the  skin,  for  the  purpose 
of  holding  their  young,  or  of  receiving  them  on  the  approach 
of  danger.     Such  are  the  Kanguroo  and  Opossum. 

Questions. — 1.  By  what  are  animals  of  the  class  Mammalia  dis- 
tinguished ?  2.  Why  is  man,  as  an  object  of  natural  history,  arranged 
with  this  class  ?     3.  From  a  regard  to  what  parts  of  animals  of  thif 


BIRDS.  217 

class  have  naturalists  arranged  them  into  orders?  4.  Describe  the 
first  order  of  mammalia, — second,  &c.  5.  What  are  the  orders  of 
mammalia  according  to  Linnseus  ?  [Note.  The  distinctive  charac- 
ters of  the  Linnsean  orders  of  mammalia,  with  the  exception  of  the 
last,  depend  on  the  kind,  position,  and  number  of  the  teeth,  and  thus 
animals  of  very  different  habits  were  brought  together,  from  a  resem- 
blance in  one  comparatively  unimportant  particular.] 


LESSON  97. 


Birds. 

Ornithology,  that  branch  of  natural  history  which  describes  the 

structure,  economy,  habits,  &c.  of  birds. 
Vis'cid,  glutinous,  tenacious. 

The  immense  catalogue  of  the  species  of  birds,  and  the 
variety  and  beauty  of  their  external  characters,  have  made 
them  favourite  objects  of  investigation  with  the  natural  his- 
torian. The  extraordinary  degree  of  instinct  displayed  in 
all  (heir  habits  and  economy,  more  especially  in  the  con- 
struction of  their  nests,  the  care  of  their  young,  and  the 
conduct  of  their  migrations,  have  called  forth  the  admiration 
of  the  philosopher  and  the  lover  of  nature.  The  splendid 
colouring  of  their  plumage,  the  powers  of  melody,  and  the 
liveliness  and  docility  of  many  species,  have  given  them 
value  as  objects  of  beauty  and  entertainment. 

The  class  of  birds  is  divided,  according  to  their  structure 
and  habits  of  life,  into  six  orders.  Birds  of  prey,  or  rapa- 
cious birds  [accip'itres)  correspond,  in  many  respects,  with 
the  carnivorous  animals  among  quadrupeds.  They  are  dis- 
tinguished by  their  strong,  hooked  beaks,  and  their  crooked 
and  powerful  talons.  •  They  are  particularly  remarkable  for 
the  very  great  distance  at  which  they  perceive  their  prey, 
and  the  accuracy  with  which  they  direct  their  flight  towards 
it.  Besides  the  upper  and  under  eye-lids,  all  birds  have  a 
third  which  is  semi-transparent,  and  serves  the  purpose  of 
protecting  the  eye  from  the  contact  of  external  bodies,  or 
from  too  powerful  light,  whilst  at  the  same  time  it  does  not 
prevent  them  from  distinguishing  the  objects  around  them. 
This  membrane  is  situated  at  the  inner  angle  of  the  eye, 
and  is  drawn  over  the  globe  of  it,  like  a  curtain,  at  will.  It 
19 


218  BIRDS. 

is  by  means  of  this  protection,  that  the  eagle  is  enabled  to 
look  steadily  at  the  sun. 

Sparrows  [Pas' seres)  form  the  most  extensive  and  nume- 
rous order,  embracing  a  great  variety  of  species,  which  differ 
so  much  among  themselves,  as  to  be  hardly  capable  of  an 
intelligible  description,  common  to  them  all.  To  this  order 
belong  those  species  which  are  most  celebrated  for  the  sweet- 
ness and  harmony  of  their  notes ;  and  in  general  the  organ 
of  voice  in  them  is  larger  and  better  formed,  than  in  any 
others.  Among  them  are  the  robin,  the  swallow,  the  linnet, 
the  humming-bird,  and  the  nightingale. 

The  third  order  {Scanso'rcs,  Climbers)  includes  those  birds 
that  have  the  external  toe  upon  each  side  turned  backwards, 
which  enables  them  to  grasp  substances  more  firmly,  and 
affords  them  a  more  sure  support,  than  other  birds.  Among 
them  are  the  woodpecker,,  the  cuckoo,  and  the  parrot. 
Woodpeckers  are  furnished  with  a  long  and  slender  tongue, 
covered  towards  its  tip  with  spines  or  bristles,  which  are 
turned  backwards,  and  coated  with  a  thick  viscid  secretion. 
They  run  in  every  direction  around  the  trunks  and  branQ,hes 
of  trees,  striking  them  with  their  beaks,  and  thrusting  their 
tongues  into  holes  and  clefts,  for  the  purpose  of  drawing  oUt 
their  food. 

The  Gallinaceous  birds  [Gallina' cecs)  have  short  and  weak 
wings,  and,  of  course,  they  are  not  constructed  for  long  and 
continued  flight.  Of  this  order  are  the  peacock,  the  turkey, 
the  pigeon  and  the  common  fowls.  The  pigeons  form  in 
some  particulars  an  exception  to  the  general  characteristics 
of  their  order.  They  fly  very  well,  live  in  pairs,  and  build 
their  nests  upon  trees  or  in  the  clefts  of  rocks.  The  most 
remarkable  species  among  them  is  the  crowned  pigeon  of 
the  Molucca  islands,  which  is  equal  in  size  to  a  turkey.  Its 
voice  is  exceedingly  loud  and  harsh,  "and  is  said  to  have 
frightened  sailors  who  landed  on  the  islands  which  it  in- 
habits, by  its  resemblance  to  the  yells  of  the  savage  natives. 

The  Waders  {Gral'lce,)  otherwise  called  shore  birds  are 
distinguished  by  their  very  long  and  naked  legs,  which  per- 
mit them  to  wade  to  a  considerable  depth  in  the  water  with- 
out wetting  their  feathers.  All  birds  with  this  structure  are 
not,  properly  speaking,  waders  in  their  habits,  though  they 
are  ranked  in  this  order.  Among  them  are  the  heron,  plo- 
ver, oxeye.  and  ostrich.     The  ostrich  is  almost  incapable  of 


REPTILES.  219 

flight,  but  runs  with  immense  rapidity.  Its  height  varies 
from  six  to  eight  feet  j  it  is  the  most  lofty  of  birds  and  the 
swiftest  of  all  animals. 

The  toes  of  Web-footed  birds  (An'sercs,)  are  connected 
together  by  a  membrane,  which  fits  them  for  being  used  as 
oars.  Their  whole  structure  is  such  as  to  adapt  them  for 
swimming  :  their  legs  are  situated  far  back  upon  their  bodies, 
their  feathers  are  thick,  smooth  and  oily,  and  their  skin  be- 
neath covered  with  a  layer  of  close  down,  which  effectually 
protects  them  from  the  contact  of  water.  Most  of  them  are 
capable  of  lofty  and  long  continued  flight,  as  the  wild  goose 
and  duck  ;  whilst  others  from  the  shortness  of  their  wings 
can  scarcely  raise  themselves  into  the  air,  but  are  principal- 
ly confined  to  the  surface  of  the  water. 

As  quadrupeds  cast  their  hair,  so  all  birds  every  year  ob- 
tain a  new  covering  of  feathers  ;  this  is  what  is  termed 
moulting.  During  its  continuance,  they  always  appear 
sickly  and  disordered ;  no  feeding  can  maintain  their 
strength,  for  their  nourishment  is  now  consumed  and  ab- 
sorbed in  administering  a  supply  to  the  growing  plumage. 
It  is  worthy  of  observation,  that  of  the  vast  number  of  birds 
which  inhabit  the  globe,  it  has  never  been  discovered  that  a 
single  one  is  of  a  poisonous  nature.  They  differ  very  much 
in  being  more  or  less  salutary  and  palatable,  as  an  article  of 
diet ;  but  none  of  them  are  pernicious.  Sea-faring  people 
and  travellers  eat  every  species  of  egg  without  the  smallest 
hesitation. 

Questions. — 1  What  renders  birds  objects  of  intsrest  to  the  natu- 
ralist and  philosopher  ?  2.  Describe  the  first  order  of  birds.  3.  Second. 
4.  Third.  5.  Fourth.  6.  Fifth.  7.  Sixth.  8.  What  is  said  of  their 
moulting  ?  9.  What  is  worthy  of  observation  respecting  them  .''  10, 
What  are  the  Linnsean  orders  of  birds  ?  (see  Appendix.) 


LESSON  98. 

Reptiles  and  Fishes. 
Icthyol'ogy,  that  branch  of  natural  history  which  treats  of  fishes. 
Reptiles  have  less  intelligence,  fewer  faculties,  and  less  in- 
stinct, than  either  quadrupeds  or  birds.    They  are,  in  general, 
sluggish  and  indolent  in  their  habits  of  life,  and  obtuse  in 
their  sensations.     In  cold  countries  they  pass  the  greater 


220 


FISHES. 


part  of  the  winter  in  a  dormant  state.  They  are  arranged 
in  four  orders.  The  Tortoises  {Chclo'nia)  liave  a  covering 
consisting  of  an  upper  and  under  shell,  joined  at  their  sides 
into  one,  which  permits  only  their  head  and  other  extremi- 
ties to  be  extended  without  it.  They  have  no  teeth  but 
their  jaws  are  armed  with  a  tough  horny  substance  which 
supplies  their  place.  The  order  of  Lizards  {Sau'ria)  in- 
cludes a  very  considerable  variety.  The  greater  part  of 
them  have  four  feet,  but  a  iew  are  possessed  of  only  two. 
They  have  nails  and  teeth,  and  their  skin  is  covered  with 
scales.  Among  them  are  the  crocodile,  the  alligator,  the 
chameleon,  the  true  lizards  and  the  dragons.  The  crocodile 
is  the  most  celebrated.  It  is  from  twenty  to  thirty  feet  in 
length  including  the  tail,  and  is  covered  with  a  coat  of 
scales,  which  on  the  back  form  an  armour  proof  against  a 
bullet,  and  have  an  appearance  like  that  of  carved  work. 
The  Serpents  {Ophid'ia)  are  distinguished  by  their  long 
and  slender  bodies  without  limbs,  and  by  the  great  extensi- 
bility of  their  jaws,  mouth  and  throat.  They  are  divided 
into  the  venomous  and  those  that  are  not  venomous.  The 
number  of  the  latter  is  the  greatest  and  includes  the  largest 
animals.  The  venomous  serpents  are  generally  armed  with 
fangs  for  the  specific  purpose  of  infusing^  poison  into  the 
wounds  they  inflict.  When  the  tooth  pierces  the  flesh  of 
any  animal,  the  poisonous  fluid  is  injected  into  the  opening. 
When  broken  or  injured,  these  fangs  are  renewed,  and 
when  not  employed,  are  hidden  from  the  sight  by  a  fold  or 
projection  of  the  gum.  Serpents  cast  their  skins  annually, 
and  the  beauty  and  lustre  of  their  colours  are  then  highly 
augmented.  The  reptiles  of  the  fourth  order  (Batrach'ia, 
frog,  salamander,  &c.)  are  principally  remarkable  for  a 
transformation  which  takes  place  in  their  offspring  after 
leaving  the  egg.  When  first  hatched,  they  are  strictly  an 
aquatic  animal,  and  capable  of  breathing  and  living  only 
under  water.  In  this  state  they  are  seen  by  thousands,  of  a 
dark  colour,  with  round  bodies,  swimming  about  in  brooks 
and  small  ponds.  After  a  certain  period,  their  form  and 
structure  are  altered,  and  they  become  at  once  animals 
capable  of  breathing  only  in  air. 

Fishes  being  destined  to  inhabit  only  the  water,  are  pro- 
vided with  organs  and  a  structure  adapted  to  the  element  in 
which  they  reside.     Since  they  cannot  breathe  pure  air,  they 


STRUCTURE    OF    INSECTS.  2^1 

have  a  peculiar  modification  of  the  organs  of  respiration  and 
circulation.  A  current  of  water  is  constantly  passed  over 
the  gills  by  the  action  of  the  mouth  of  the  animal,  and  by 
means  of  the  air  it  contains,  exerts  an  influence  over  the 
blood  circulating  in  them,  and  produces  the  same  changes 
in  it  as  are  produced  in  the  lungs  of  other  animals  by  the  air 
they  breathe.  A  few  fishes,  one  of  which  is  called  the  tor- 
pedo, are  possessed  of  a  very  remarkable  means  of  defence, 
which  consists  in  the  power  of  inflicting  upon  whatever  liv- 
ing creature  comes  in  contact  with  them,  a  powerful  elec- 
trical shock.  These  shocks  are  so  powerful,  that  in  South 
America,  horses  driven  into  the  pools  which  some  fishes  of 
this  kind  inhabit,  have  sometimes  been  stunned  and  even 
killed.  The  shocks  become  weaker  and  weaker  upon  con- 
tinued repetition,  till  the  animal  is  exhausted,  and  loses  for 
some  time  the  power  of  producing  any  effect. 

Questions. — 1.  What  is  said  of  reptiles?  2.- Describe  the  first 
order.  3.  The  second.  4.  The  third.  5.  The  fourth.  6.  Describe 
tlie  organs  of  respiration  and  circulation  in  fishes.  7.  What  remark- 
able means  of  defence  have  some  fishes  ^  [Note.  Fishes  are  divided 
into  orders  and  genera,  according  to  certain  diflerences  in  the  forma- 
tion, structure,  and  situation  of  their  mouth,  gills,  gill-coverings,  fins, 
&c.  : — and  they  are  called  Apodes,  as  eels,;  Jugulares,  as  cod  ;  Tho- 
racici,  as  perch ;  Mdominalcs,  as  pike  and  salmon.] 


LESSON  99. 

Structure  and  Transformation  of  Insects. 

Faucet   a  little  face  or  side  of  a  body  cut  into  a  number  of  angles. 
Hexag  onal,  having  six  sides,  or  angles. 

Lu'bricated,  made  smooth  so  as  easily  to  glide  over  any  part. 
Entomology,  that  branch  of  natural  history  which  treats  of  insects. 

The  animals  of  this  class  are  remarkable  for  a  greater 
variety  of  powers  and  a  more  wonderful  display  of  instinct 
and  intelligence,  than  any  other  of  the  invertebral  animals. 
They  are  distinguished  by  many  peculiarities  of  form.  In- 
stead of  a  heart,  insects  have  a  vessel  or  reservoir  situated 
along  the  back,  extending  from  one  end  of  their  bodies  to 
the  other,  and  filled  with  a  transparent  fluid,  which  is  sup- 
posed to  answer  the  purpose  of  blood,  and  to  be  conveyed, 
by  absorption,  to  the  various  organs.  They  have  no  parti- 
19* 


TRANSFORMATION    OF    INSECTS 

cular  organ  for  respiration,  but  their  bodies  are  penetrate^ 
in  every  direction  by  tubes,  through  which  the  air  is  trans 
rnitted  to  every  part.  These  tubes  communicate  externally 
by  openings  called  spiracles.  To  serve  the  purpose  of  a  brain 
and  nervous  system,  they  are  furnished  with  two  knottea 
cords  running  the  length  of  the-ir  bodies.  They  possess  the 
senses  of  seeing,  tasting,  smelling,  and  feeling  ;  but  organs 
of  hearing,  if  they  exist,  have  not  yet  been  discovered.  They 
are  provided  with  a  hard  external  covering  which  differs  in 
different  species ;  in  some  it  forms  a  complete  case  of  a 
horny  or  shell-like  substance  ;  and  in  others  it  consists  merely 
in  a  tough  muscular  coat,  divided  into  rings  which  surround 
the  body.  Their  heads  are  furnished  with  anten'no)  or  feel- 
erSj  which  are  a  kind  of  filaments  composed  of  joints,  de- 
signed probably  as  the  organs  of  the  sense  of  touch,  or  of 
sensations  still  more  delicate  and  of  a  nature  totally  unknown 
to  us. 

The  mouth  oT  insects  varies  much  in  construction,  ac- 
cording to  the  nature  of  their  food.  Some  are  armed  with 
a  sort  of  lancet,  and  others  with  a  trunk  or  probos'cis,  which 
in  the  butterflies  is  capable  of  being  rolled  up  in  a  spiral 
form.  Their  eyes  may  be  considered  among  the  most  sur- 
prising of  nature's  works.  Tiiey  differ  much  in  form  and 
colour  in  the  different  insects  ;  but  they  are  not,  as  might 
be  at  first  supposed,  mere  hemispherical  bodies  of  plane  sim- 
ple surfaces,  for  examination  proves  them  to  be  composed  of 
an  immense  assemblage  of  highly  wrought  hexagonal  facets, 
each  furnished  with  its  proper  optic  nerve,  retina,  and  other 
parts  necessary  for  vision  :  the  number  of  these  facets  dif- 
fers in  different  species  ;  eight  thousand  have  been  counted 
in  the  eye  of  the  common  fly,  and  twelve  thousand  in  that 
of  the  dragon  fly. 

How  sweet  to  muse  upon  His  skill  displayed  ! 
Infinite  skill !  in  all  that  he  has  made, 
To  trace  in  Nature's  most  minute  design 
The  signature  and  stamp  of  Power  Divine  ; 
Contrivance  exquisite  expressed  v/ith  ease, 
Where  unassisted  sight  no  beauty  sees ; 
The  shapely  limb,  and  lubricated  joint 
Within  the  small  dimensions  of  a  point ; 
Muscle  and  -n^rve  miraculously  spun, 


TRANSFORMATION    OP    INSECTS.  2123 

His  mighty  work  who  speaks,  and  it  is  done. 
Th'  Invisible  in  things  scarce  seen  revealed ; 
To  whom  an  atom  is  an  ample  field.         Cowpeu. 

The  greater  part  of  insects  are  winged.  Those  which 
are  not  winged,  continue,  during  their  whole  existence,  of 
the  same  form  and  structure  as  at  birth.  Those  which  are 
winged  undergo  certain  changes  of  form,  which  are  called 
their  tnetamor' phases.  They  differ  in  number  in  different 
kinds  of  insects.  For  an  example  we  may  take  the  tribe  of 
the  Butterfly.  From  the  egg  of  this  insect  is  hatched  an 
animal  differing  entirely  from  its  parent.  Its  body  is  long 
and  cylindrical,  and  divided  into  numerous  rings.  It  is  pro- 
vided with  a  large  number  of  very  short  legs,  with  jaws,  and 
with  several  small  eyes.  It  is  familiarly  known  to  us  by  the 
name  of  caterpillar.  It  lives  in  this  state  a  considerable 
time,  subsisting  upon  such  food  as  is  adapted  to  its  nature. 
At  length  it  casts  off  its  skin,  and  appears  in  another  form 
without  limbs.  It  ceases  to  feed  or  to  move.  It  seems  to  be 
totally  without  life.  This  is  called  the  clirys'alis.  After  a 
while,  by  examining  it  closely,  the  imperfect  shape  of  a  but- 
terfly may  be  distinguished  through  its  surface  ;  and  finally 
the  envelope  is  broken  and  the  animal  escapes.  Its  wings 
are  at  first  short,  weak,  and  moist,  but  they  soon  unfold  to  a 
greater  size,  and  become  strong  ;  and  the  insect  is  in  a  state 
to  fly.  It  has  now  six  long  legs,  a  spiral  trunk,  two  antennce, 
and  eyes  diflering  entirely  from  those  of  the  caterpillar.  In 
short,  it  is  an  animal  totally  different,  delighting  us  by  the 
beauty  of  its  spots  and  the  variety  of  its  colours  ;  and  yet 
these  wonderful  changes  are  only  the  successive  unfolding 
of  parts  contained  one  within  another  in  the  original  em'bryo. 

In  the  first  state  the  animal  is  called  the  larva;  in  the  se- 
cond the  cJiri/salis  or  nympha;  and  the  third  is  called  the 
perfect  state.  A  considerable  portion  of  the  insect  tribes 
pass  through  these  three  changes  of  existence.  But  many 
only  undergo  what  is  called  a  demi-metamorphosis.  Their 
larva  resembles  the  perfect  insect,  except  that  it  has  no  wings. 
And  the  only  change  they  experience  is,  that  in  the  nymph 
state  they  have  the  rudiments  of  wings,  which  finally  on 
casting  their  skins,  are  changed  into  complete  ones.  Such 
are  grasshoppers  and  many  others. 
When  about  to  pass  into  the  chrysalis  state,  which  is  a 


224  TRANSFORMATION    OF    INSECTS. 

State  of  imbecility,  insects  select  the  most  proper  places  and  j 

modes  of  concealing  themselves  from  their  enemies.     Some,  j 

as  the  silk-worm  and  others,  spin  silken  webs  round  their  \ 

bodies,  by  which  the  animal  form  is  completely  disguised.  : 

Others  leave  the  plants  upon  which  they  formerly  fed,  and  j 

hide  themselves  in  little  cells  which  they  make  in  the  earth.  | 

Some  fix  themselves  by  a  gluten,  and  spin  a  rope  round  their  | 

middle  to  prevent  them  from  falling.     Others  attach  them-  ' 

selves  to  walls,  with  their  heads  higher  than  their  bodies,  but  , 

in  various  inclinations.     In  this  state  many  remain  motion-  ; 

less  and  seemingly  inanimate,  during  the  whole  winter.  | 

Behold  the  insect  race,  ordained  to  keep  i 

The  lazy  Sabbath  of  a  half  year's  sleep  ;  i 

Entombed,  beneath  the  filmy  web  they  lie,  i 

And  wait  the  influence  of  a  kinder  sky.  ^■ 

When  vernal  sun-beams  pierce  their  dark  retreat,  i 

The  heaving  tomb  distends  with  vital  heat ;  .; 
The  full  formed  brood  impatient  of  their  cell,             "Mr^ 

Start  from  their  trance  and  burst  their  silken  shell ;  *^  ^ 

Trembling,  awhile  they  stand,  and  scarcely  dare  s 

To  launch  at  once  upon  the  untried  air  :                       ^  i 
At  length  assured,  they  catch  the  favouring  gale,       jp« 

And  leave  their  sordid  spoils  and  high  in  ether  sail.  ™  ^ 

Barbauld.  ; 

Questions — 1.  For  what  are  insects  remarkable  ?   2.  What  havo  j 

they  instead  of  a  heart  ?    3.  What  have  they  to  answer  the  purpose  [ 

of  a  respiratory  organ  ?    4.  Brain  and  nervous  system?    5.  What  is  j 

said  of  their  senses  and  external  covering  ?    C.  What  are  antennae  ?  ^ 
7.  Describe  the   eyes  of  insects.    8.  What   are  the  changes  called 
which   winged  insects  undergo  ?     9.   Give   a  description    of    these 

changes  in  the  example  of  the  butterfly.    10.  What  is  tlie  animal  ! 

called  in  its  first — second — ^third  state  .^    11.  Describe  what  is  called  i 
domi-metamorphosis.    12.  What  are  some  of  the   artifices  of  insects 

when  about  to  enter  the  chrysaUs  state  ?     [Note.    All  insects  have  'j 

six  legs,  with  the  exception  of  the  millepedes,  (pronounced  mil'le-  j 

pedz,  or  mil-lep'e-dez)  which  have  always  more,  and  the  number  in-  | 

creases  also  with  their  age.     ^ur clia  a.nd    Chrysalis  nre   synonymous:  • 
words,  both  alluding  to  the  metallic  or  golden  splendour  of  the  case  in 

which  insects  are   enclosed  during  that  state.     This  brilliancy  how-  \ 

ever  seems  to  be  confined  to  the  butterfly  tribe.     The  name  Pupa  has  « 
lately  been  substituted  for  chrysalis  and  aurelia,  because  many  insects 

in  this  state  are  thought  to  resemble  an  infant  in  swaddling  clothes.  \ 


ORDERS  OF  INSECTS.  225 


LESSON  100. 

Orders  of  Insects. 

Per'forator,  a  part  of  some  insects  with  which  they  bore  various 

substances  in  order  to  admit  tlieir  e^gs. 
Farina'ceous,  mealy,  resembling  the  farina  of  flowers. 

LiNN^us  divided  insects  into  seven  orders.  His  divisions 
are  founded  upon  the  presence  or  absence  of  wings,  their 
number,  their  texture,  their  arrangement,  and  the  nature  of 
their  surface.  1^\\g  first  order  {colcop'tera)  has  four  wings. 
The  upper  pair  consist  of  a  hard,  crustaceous  or  horny  sub- 
stance, and  cover  or  defend  the  under  pair,  which  are  of  a 
more  soft  and  flexible  texture,  and  are  folded  beneath  them. 
This  is  the  most  numerous  and  best  known  kind  of  insects  ; 
and  many  of  them  are  very  remarkable  for  the  singularity 
of  their  forms  and  the  beauty  of  their  colours.  The  various 
insects  known  under  the  name  of  beetles  and  winged  bugs 
are  included  in  this  order. 

The  second  order  (Jicmip'tera)  has  likewise  four  wings  ; 
but  the  upper  pair  is  not  of  so  hard  a  texture  as  those  of  the 
beetle  tribe.  They  are  more  like  fine  vellum,  and,  at  their 
extremities,  terminate  with  a  membranous  edge,  which  re- 
sembles the  substance  of  the  under  pair.  They  cover  the 
body  horizontally,  and  do  not  meet  in  a  straight  line  or 
ridge,  as  they  do  in  the  first  order.  Among  them  are  found 
the  grasshopper  and  the  locust. 

The  third  order  {Icpidop'tera)  has  four  wings  and  com- 
prehends the  various  kinds  of  moths  and  butterflies.  Their 
wings  are  covered  with  a  farinaceous  powder,  or  rather  with 
scales  or  feathers,  disposed  in  regular  rows,  nearly  in  the 
same  manner  as  tiles  are  laid  upon  the  roofs  of  houses. 
The  elegance,  the  beauty,  the  variety  of  colours,  exhibited 
in  their  wings,  are  produced  by  the  disposition  and  tincture 
of  these  minute  feathers.  When  the  feathers  are  rubbed 
off,  the  wings  appear  to  be  nothing  more  than  a  naked  and 
often  a  transparent  membrane. 

T\ie  fourth  ox&er  {neurop'tera)  hdiS  four  naked  membra- 
nous wings,  which  are  so  interspersed  with  delicate  veins, 
that  they  have  the  appearance  of  a  beautiful  net  work.  They 
have   no  sting.     Of  this  order  are  the  various  species  of 


2^6  ORDERS  OF  INSECTS. 

dragon  fly,  large  and  well  known  insects  that  frequent 
lakes  and  pools  of  stagnant  water  ;  the  Ephem'eral  flies, 
which  pass  two  or  three  years  in  the  states  of  larva  and 
chrysalis,  but  whose  existence  as  winged  and  perfect  in- 
sects is  limited  to  a  single  day ;  and  the  Ant-lion  and  Ter'- 
mites,  the  former  celebrated  as  the  destroyer  of  the  common 
ant,  and  the  latter  for  the  ravages  they  make  in  some  tro- 
pical countries. 

The  Jifih  order  {liymcnop'tera)  has  four  naked  mem- 
branous wings,  but  destitute  of  that  delicate,  netted  struc- 
ture, which  belongs  to  the  last  order.  The  females  have 
either  a  perforator  or  a  sting.  In  the  domestic  economy 
and  mode  of  propagation  of  some  of  the  species,  there  are 
circumstances  which  excite  our  admiration  and  astonish- 
ment. The  ant,  wasp,^nd  bee  belong  to  this  order.  They 
live  in  societies,  greater  or  less  in  extent  and  number;  and 
prepare  habitations  and  nourishment  for  themselves  and 
offspring,  with  a  forethought  and  provident  care,  excelled 
only  by  man  himself.  In  some  of  the  tribes  of  this  order, 
there  is,  beside  the  males  and  females,  a  third  sort  called 
neuters,  as  among  the  ants  and  bees. 

The  sixth  order  (dip'tera)  has  only  two  wings,  but  be- 
neath them  are  two  cylindrical  projections,  which  seem  as 
if  they  were  the  rudiments  of  another  pair.  These  have 
been  called  balancers  or  poisers,  from  being  supposed  to  aid 
them  in  preserving  an  equilibrium  during  their  flight.  Be- 
tween them  and  the  wings  themselves  are  found  small  mem- 
branous scales,  one  upon  each  side,  against  Avhich  the 
balancer  strikes  with  great  rapidity,  whilst  the  insect  is  in 
motion,  and  causes  that-  buzzing  which  is  then  observed. 
To  this  order  belong  some  of  the  most  troublesome  and  an- 
noying of  the  whole  animal  creation,  such  as  the  various 
species  of  gnat,  and  the  common  fly.  They  are  found  in 
almost  every  part  of  the  globe. 

The  seventh  and  last  order  of  insects  (ap'tera)  includes  a 
great  variety  that  are  destitute  of  wings.  It  is  true  that  in 
the  preceding  orders  are  arranged  many  sorts  of  insects  that 
are  destitute  of  wings,  but  they  are  so  arranged  because  in 
their  general  structure  and  habits  of  life  they  resemble  the 
other  members  of  the  order.  Tlie  Aptera,  however,  have 
no  such  resemblance,  and  are  therefore  placed  by  them- 
selves.    Some  animals  of  this  order  cover  the  surface  of 


ORDERS  OP  INSECTS.  227 

plants  so  completely  as  to  produce  the  appearance  of  a  dis- 
coloured change  of  structure. 

The  family  of  spiders  (ara'nea)  is  not  always  arranged 
^among  insects,  and  strictly  speaking  their  structure  is  dif- 
ferent in  some  important  particulars.  They  are  distinguish- 
ed from  all  other  insects  by  the  absence  of  the  antennae. 
They  have  generally  eight  legs,  and  are  furnished  with  six 
or  eight  eyes,  which  enable  them  to  see  objects  in  several 
different  directions  at  once.  They  are  nourished  generally 
by  living  prey,  which  they  secure  by  means  of  a  web,  spun 
with  much  ingenuity.  The  threads,  of  which  the  web  is 
compo'sed,  are  produced  from  six  little  fleshy  bunches,  or 
muscular  instruments,  each  of  which  contains  about  a 
thousand  tubes,  or  outlets  of  threads,  so  extremely  minute 
that  many  hundreds  of  them  must  be  united  before  they 
form  one  of  those  visible  ropes,  of  which  the  spider's  web  is 
composed.  By  means  of  their  webs,  many  species  of  spi- 
ders, particularly  when  young,  are  able  to  transport  them- 
selves to  a  considerable  distance  through  the  air.  In  order 
to  effect  this,  they  ascend  some  eminence,  and  throw  out  a 
number  of  webs.  These  are  raised  up  and  carried  along  by 
the  wind,  and  the  animal  being  buoyed  up  by  them  is  conveyed 
sometimes  to  a  great  height.  In  order  to  alight,  they  have 
only  to  disengage  themselves  from  a  part  of  their  web,  and 
suffer  themselves  to  descend  gradually  to  the  ground.  It  is 
probable  that  they  have  recourse  to  this  expedient,  in  part 
at  least,  for  the  purpose  of  catching  insects  for  food.  In 
autumn,  the  air  is  often  full  of  the  cobwebs  which  have  been 
made  use  of  for  this  singular  mode  of  conveyance.  This 
fine  filmy  substance  is  called  Gossamer ;  and  it  is  seen  not 
only  in  the  air,  but  is  more  observable  in  stubble  fields,  and 
upon  furze  and  other  low  bushes.  Those  who  have  ascend- 
ed eminences  for  the  purpose  of  observing  the  phenomenon, 
have  frequently  seen  spiders  floating  by  in  the  air,  supported 
in  the  manner  which  has  been  described. 

To  the  Insect  of  the  Gossamer  .••—By  C.  Smith. 

Small,  viewless  aeronaut,  that  by  the  line         ^ 
Of  Gossamer  suspended,  in  mid  air 
Float'st  on  a  sunbeam.     Living  atom,  where 
Ends  thy  breeze-guided  voyage  1  With  what  desig« 
In  ether  dost  thou  launch  thy  form  minute, 


228  CRUSTACEOUS   ANIMALS. 

Mocking  the  eye  ?  Alas  !  before  the  veil 

Of  denser  clouds  shall  hide  thee,  the  pursuit 

Of  the  keen  swift  may  end  thy  fairy  sail. 

Thus  on  the  golden  thread  that  fancy  weaves 
Buoyant,  as  Hope's  illusive  dattery  breathes, 

The  young  and  visionary  poet  leaves 

Life's  dull  realities,  while  seven-fold  wreathes 

Of  rainbow  light  around  his  head  revolve. 

Ah  !  soon  at  Sorrow's  touch  the  radiant  dreams  dissolve. 

Questions. — 1.  Upon  what  is  the  division  of  insects  into  orders 
ounded  ?  2.  What  are  the  characteristics  of  the  first  order  ?  .3.  Se- 
cond ?  4.  Third  ?  5.  Fourth  ?  C.  Fifth  ?  7.  Sixtli  ?  8.  Seventh  •" 
9.  Describe  the  wings  of  butterflies.  10.  Describe  ephemeral  flies.-* 
IL  What  is  worthy  of  notice  in  ants,  wasps,  and  bees  ?  12.  How  is 
the  buzzing  of  flies  produced  i  13.  How  do  aptera  insects  often  ap- 
pear on  plants  .''  14.  How  are  spiders  distinguislied  from  all  other 
insects  'i  15.  How  is  the  web  of  the  spider  produced  .''  16.  Describe 
the  aerial  excursions  of  spiders.  17.  What  is  the  gossamer,  and  where 
seen .' 


LESSON  lOL 

Crustaceous  and  3IoUuscous  Animals. 

Mu'cous,  slimy,  viscous  or  glutinous. 

The  Crustaceous  animals  have  been  sometimes  included 
in  the  class  of  insects,  to  which  they  have  indeed  many 
strong  points  of  resemblance.  They  deserve,  however,  a 
separate  consideration,  both  on  account  of  their  size  and  im- 
portance, and  of  some  anatomical  differences  of  structure. 
They  have  articulated  limbs,  antennas,  and  jaws,  similarly 
formed  to  those  of  insects.  But  they  breathe  by  means  of 
gills,  and  have  a  regular,  double  circulation  ;  in  which  par- 
ticulars they  difer  from  insects.  Among  the  most  familiar 
examples  of  this  classL  are  the  lobster,  craw-lish,  and  what 
is  usually  called  the  horse-shoe.  They  are  covered  by  a 
pretty  thick,  firm  shell,  which  envelopes  them  completely. 
As  this  shell  is  incapable  of  growth,  it  is  occasionally  chang- 
ed, to  make  room  for  the  constant  increase  in  size  of  the 
aniiflal.  It  is  thrown  off,  and  their  bodies  remain  for  a  time 
entirely  naked,  and  exposed  in  a  soft  and  defenceless  state. 


MOLLUSCOUS   ANIMALS.  2^ 

In  this  case,  the  animal  generally  retires  to  some  place  ot 
concealment  and  security,  and  remains  till  the  shell  is  re- 
stored by  the  deposition  of  calcareous  matter  on  the  exter- 
♦nal  membrane  of  the  skin,  which  becomes  hard  and  firm, 
and  finally  takes  the  place  of  the  old  shell. 

The  Molluscous  animals  form  a  large  and  extensive  class, 
but  their  structure,  residence,  and  habits,  are  obscurely  and 
imperfectly  known.  Among  them  are  the  cuttle-fish,  oyster, 
clam,  snail,  and,  in  short,  nearly  all  the  testaceous  animals, 
or  shell-fish,  as  they  are  usually  called,  although  they  have 
no  resemblance  to  fishes,  and  do  not  all  inhabit  the  water. 
They  are  destitute  of  bones  and  articulated  limbs.  Their 
bodies  are  generally  of  a  soft  texture,  and  frequently,  at  first 
sight,  appear  to  be  little  else  than  a  simple  mucous  mass, 
without  parts  and  almost  without  organization.  In  most  in- 
stances they  are  completely  enveloped  in  a  fold  or  reflection 
of  the  skin,  which  is  called  their  mantle.  Sometimes  there 
is  only  this  simple  membranous  covering ;  but  more  fre- 
quently there  is  a  hard  external  shell,  which  serves  as  a  re- 
treat into  which  the  animal  may  withdraw  itself,  and  which 
it  can  carry  about  in  all  its  changes  of  place.  These  shells 
difter  exceedingly  in  shape,  colour,  and  texture,  in  different 
species,  and  among  them  are  found  some  whose  form,  polish, 
and  splendid  tints  place  them  among  the  most  beautiful  ob- 
jects in  nature. 

Questions. — 1.  Tn  what  points  do  crustaceoiis  animals  resemble  in- 
sects ?  2.  In  what  do  they  differ  ?  3.  What  are  examples  of  this 
class.'  4.  What  is  said  of  the  growth  and  casting  of  their  shell?  5. 
What  are  examples  of  molluscous  animals  ?  6.  What  description  of 
them  is  given  ?  7.  What  is  said  of  their  shells?  [Note.  The  study 
of  those  animals  in  the  class  mollusca  which  are  characterized  by  a 
shell  or  calcareous  covering  has  obtaitied  the  distinct  scientific  name 
of  Conchology.  The  objects  of  conchology  are  separated  into  three 
divisions,  namely,  m2//<i?;«Z?;e5,  or  shells  with  many  valves  ;  bivalves^ 
or  sheila  with  two  valves ;  univalves,  or  shells  with  one  valve.] 
20 


290  ZOOPHYTES. 


LESSON  102. 


Vermes  and  Zoophytes.  I 

Tentac'ula,  often  called  feelers ;  organs  supplying  the  place  of 
hands  and  arms  to  some  animals,  and  intended  also  for  feeling. 
(Singular,  Tentaculum.) 

The  term  Ver'mes  has  been  used  with  great  vagueness  in 
natural  history,  and  employed  to  designate  animals  to  which 
the  name  was  not  appropriate.  It  is  now,  however,  more 
restricted  in  its  application,  and  is  made  to  include  only  a 
small  class  of  animals.  Their  bodies  are  of  a  cylindrical, 
elongated  shape,  divided  into  a  great  number  of  rings.  In 
some  species,  certain  black  points  appear  around  the  head, 
which  have  been  supposed  to  be  eyes,  but  this  is  doubtful. 
They  are  the  only  invertebral  animals  which  have  red  blood. 
It  circulates  in  a  double  system  of  vessels,  but  there  is  no 
distinct  fleshy  heart  to  give  it  motion.  They  breathe  by 
means  of  gills,  which  are  sometimes  within  and  sometimes 
without  their  bodies.  They  have  no  limbs,  but  on  each  of 
the  rings  of  which  their  bodies  are  composed,  are  little 
spines  or  bristly  projections  which  answer  in  some  sort  the 
purpose  of  feet.  All,  except  tlie  earthworm,  inhabit  the 
water.  Many  of  them  bury  themselves  in  the  sand  ;  some 
form  themselves  a  sort  of  tube  or  habitation  of  sand,  or  other 
materials  ;  and  others  exude  from  their  surfaces  a  calcareous 
matter,  which  produces  a  shell  around  them.  When  cut 
through  the  middle,  each  portion  becomes  a  distinct  in- 
dividuals 

There  are  several  species  of  the  leech,  of  which  the  me- 
dicinal leech  is  the  most  valuable.  It  has  three  jaws  or  ra- 
ther lancets,  with  which  it  pierces  the  skin  of  animals,  in 
order  to  draw  their  blood.  Its  tail  is  furnished  with  a  shal- 
low cup,  by  which  it  is  able  to  fix  itself  firmly  to  different 
objects,  while  obtaining  its  nourishment ;  and  by  means  of 
the  same  organ  it  mov^s  from  place  to  place. 

The  class  of  Zo'ophytes  is  the  last  division  of  the  animal 
kingdom,  and  the  lowest  in  the  scale  of  the  animated  crea- 
tion. It  includes  an  immense  number  of  individuals  but 
imperfectly  known,  and  having  but  few  points  of  resem- 
blance and  connexion  with  one  another.  In  general,  they 
have  no  nervous  system,  no  complete  vascular  circulation, 


5iOOPHYTES.  5§l 

no  distinct  apparatus  for  respiration,  and  no  sense  but  that 
of  feeling  and  perhaps  that  of  tasting.  This  is  not  true, 
however,  without  exception ;  for,  in  some  instances,  traces 
'  of  a  nervous  system,  of  a  circulation,  and  of  respiratory  or- 
gans, may  be  detected,  as  in  the  sea-urchin,  the  common 
star-fish,  and  the  sea-egg.  These  Zoophytes  are  the  most 
perfect  in  their  structure,  and  are  endowed  with  a  curious 
set  of  organs  for  the  purpose  of  motion.  Their  shells  are 
pierced  with  a  large  number  of  holes,  regularly  arranged, 
through  which  project  the  feet  of  the  animal,  or  rather  the 
instruments  answering  the  purpose  of  feet.  These  are  little 
hollow  cylinders,  filled  with  a  liquid,  and  terminating  in  a 
kind  of  knob,  which  is  also  hollow.  By  forcing  the  liquid 
into  these  cylinders,  or  by  exhausting  it  from  them,  the  ani- 
mal can  either  lengthen  or  shorten  them.  The  knob,  when 
exhausted,  is  drawn  into  a  cup-like  form,  and  thus  may  be 
firmly  fixed  to  whatever  object  it  is  applied,  like  a  cupping- 
glass  ;  and  when  the  liquid  is  again  thrown  into  it,  it  is 
again  loosened. 

Pol'ypes  have  a  hollow,  cylindrical,  or  conical  body,  with 
one  extremity  open  which  serves  for  their  mouth,  and  is  sur- 
rounded by  a  number  of  orgaps,  (icntacula)  by  which  they 
seize  their  prey.  Many  of  them  have  been  celebrated  on 
account  of  the  fact,  that  when  one  is  divided  into  several 
pieces,  each  piece  becomes  a  distinct  animal,  perfect  in  all 
its  parts.  The  immense  beds  of  coral  and  the  diflferent 
kinds  of  sponge,  are  nothing  but  the  habitations  of  infinite 
numbers  of  these  little  animals,  and  are  produced  by  their 
labour.  Corals  grow  in  such  quantities,  and  to  such  heights 
in  some  seas,  as  to  create  islands.  The  Friendly  Islands, 
in  the  Pacific  Ocean,  were  thus  raised  by  corals  from  the 
depth  of  that  sea.  Ships  have  often  been  lost  by  striking 
on  coral-rocks. 

Questions. — 1.  What  is  said  of  the  former  and  present  application  of 
the  term  Vermes  ?  2.  What  is  said  of  the  structure  of  Vermes  ?  3.  Of 
the  circulation  of  their  blood  and  of  their  respiration?  4.  Of  their  in- 
struments of  motion,  and  their  habitations  ?  5.  Describe  the  medici- 
nal Leech.  6.  What  is  said  of  the  general  structure  of  Zoophytes? 
7.  Describe  the  organs  of  motion  in  the  most  perfect  Zoophytes.  8. 
What  is  the  structure  of  Polypes  ?  9.  For  what  celebrated  ?  10.  How 
are  corals  and  sponge  produced  ?  11.  What  is  said  of  the  growth  of 
corals  in  some  seas  ?  [Note.  To  the  class  of  Zoophytes  belong  In- 
testinnl  worms,  sea-nettles,  or  sea-anem'ones,  Medusae,  or  sunfish,  an<J 


232  EXISTENCE  OF  THE  DEITY. 

Animalcules,  which  have  been  called  infusorial  animals,  {Infusoria,) 
because  they  are  principally  found  in  some  animal  and  vegetable 
fluids  and  infusions.]  12.  What  are  the  orders  of  Vermes  accordinj; 
to  Linnaeus  .-"  (see  Appendix.)  13.  In  treating  of  a  particular  animal, 
how  are  naturalists  accustomed  to  designate  it  ?    14.  Give  examples.' 


LESSON  103.  ] 

Existence  of  the  Deity.  ^^ 

God  and  the  world  which  he  has  formed  are  our  great   i 
objects.     Every  thing  which  we  strive  to  place  between  these    ; 
is  nothing.     We  see  the  universe,  and  seeing  it,  we  believe   ] 
in  its  Maker.     The  universe  exhibits  indisputable  marks  of   \ 
design :  it  is  not,  therefore,  self-existing,  but  the  work  of  a  1 
designing  mind.     From  the  great  masses  that  roll  through 
space,  to  the  slightest  atom  that  forms  one  of  their  impercep-  jj 
tible  elements,  every  thing  is  conspiring  for  some  purjjosc.  \ 
I  shall  not  speak  of  the  relations  of  the   planetary  motions    : 
to  each  other, — of  the  mutual  relations  of  the  various  parts   ? 
of  our  globe, — of  the  dilFerent  animals  of  the  ditferent  ele- 
ments, in  the  conformity  of  their  structure  to  the  qualities  of  ^ 
the  elements  which  they  inhabit, — of  man  himself  in  all  the   j 
nice  adaptation  of  his  organs  : — to  these  splendid  proofs,  it  is   j 
scarcely  necessary  to  do  more  than  to  allude.     But  when 
we  think  of  the  feeblest  and  most  insignificant   of  living 
things, — the  minutest  insect  which  it  requires  a  microscope    ' 
to  discover,  when  we  think  of  it  as  a  creature,  having  limhs  \ 
that  move  it  from  place  to  place, — nourished  by  little  vessels,    ■ 
that  bear  to  every  fibre  of  its  frame,  some  portion  of  the  food 
which  other  organs  have  rendered  fit  for  serving  the  pur-    < 
poses  of  nutrition  ; — having  senses,  as  quick  to  discern  the 
objects  that  bear  to  it   any  relative  magnitude  as   ours, — • 
and  not  merely  existing  as  a  living  piece  of  most   beautiful 
mechanism,  but  having  the  power,  which  no  mere  mechan- 
ism, however  beautiful,   ever  had,  of  multiplying   its  own 
existence,  by  the  production  of  living  machines  exactly  re- 
sembling itself; — when  we  think  of  all  the  proofs  of  con- ^ 
trivance  which  are  thus  to  be  found  in  what  seems  to  us  a 
single  atom,  or  less  than  a  single  atom,  and  when  we  think 
of  the  myriads,  and  myriads  of  such  atoms,  which  inhabit 
even  the  smallest  portion  of  that  earth,  which  is  itself  but 


POLITICAL  ECONOMY.  233 

almost  an  invisible  atom,  compared  with  the  great  system 
of  the  heavens, — what  a  combination  of  simplicity  and 
grandeur  do  we  perceive  !  It  is  one  universal  design,  or  an 
infinity  of  design ; — nothing  seems  to  us  little,  because 
nothing  is  so  little  as  not  to  proclaim  the  omnipotence  which 
made  it ; — and  I  may  say  too  that  nothing  seems  to  us 
great  in  itself,  because  its  very  grandeur  speaks  to  us  of  that 
immensity,  before  which  all  created  greatness  is  scarcely  to 
be  perceived. 

On  particular  arguments  of  this  kind,  however,  that  are 
as  innumerable  as  the  things  which  exist,  it  is  not  necessary 
to  dwell.  Those  whom  a  single  organized  being,  or  even  a 
single  organ,  such  as  the  eye,  the  ear,  the  hand,  does  not 

.  convince  of  the  being  of  a  God, — who  do  not  see  him,  not 
>^iore  in  the  social  order  of  human  society,  than  in  a  single 

"instinct  of  animals,  producing  unconsciously,  a  result  that  is 
necessary  for  their  continued  existence,  and  yet  a  result 
which  they  cannot  have  foreknown — will  not  see  him  in  all 
the  innumerable  instances  that  might  be  crowded  together 
by  philosophers  and  theologians. 

The  world,  then,  loas  made  ; — there  is  a  designing  Power 
which  formed  it — a  Power  whose  own  admirable  nature  ex- 
plains whatever  is  admirable  on  earth,  and  leaves  to  us  in- 
stead of  the  wonder  of  ignorance,  that  wonder  of  knowledge 
and  veneration  which  is  not  astonishment,  but  love  and  awe. 

Brown. 


LESSON  104. 

Political  Economy. 
Tech'nical,  belonging  to  arts ;  not  in  common  or  popular  use. 
The  language  of  science  is  frequently  its  most  difficult 
part,  but  in  political  economy  there  are  few  technical  terms, 
and  those  easily  comprehended.  It  may  be  defined  as  the 
science  which  teaches  us  to  investigate  the  causes  of  the 
wealth  and  prosperity  of  nations. 

In  a  country  of  savages,  you  find  a  small  number  of  in- 
habitants spread  over  a  vast  tract  of  land.     Depending  on, 
the  precarious  subsistence  afforded  by  fishing  and  hunting, 
they  are  frequently  subject  to  dearths  and  famines,  which  cut 
20* 


POLITICAL    ECONOMY. 

them  off  in  great  numbers.  As  soon  as  they  begin  to  appf/ 
themselves  to  pasturage,  their  means  of  subsistence  are 
brought  within  narrower  limits,  requiring  only  that  degree 
of  wandering  necessary  to  provide  fresh  pasturage  for  their 
cattle.  Their  flocks  ensuring  them  a  more  easy  subsistence, 
their  families  begin  to  increase  ;  they  lose  in  a  great  mea- 
sure their  ferocity,  and  a  considerable  improvement  takes 
place  in  their  character. 

By  degrees  the  art  of  tillage  is  discovered,  a  small  tract  of 
ground  becomes  capable  of  feeding  a  greater  relative  number 
of  people  ;  the  necessity  of  wandering  in  search  of  food  ia 
superseded ;  families  begin  to  settle  in  fixed  habitations ; 
and  the  arts  of  social  life  are  introduced  and  cultivated. 

In  the  savage  state  scarcely  any  form  of  government  is 
established  ;  the  people  seem  to  be  under  no  control  but  that 
of  their  military  chiefs  in  time  of  warfare.  The  possession 
of  flocks  and  herds  in  the  pastoral  state  introduces  property, 
and  laws  are  necessary  for  its  security  ;  the  elders  and  lead- 
ers therefore  of  these  wandering  tribes  begin  to  establish 
laws,  to  violate  which  is  to  commit  a  crime  and  to  incur  a 
punishment.  This  is  the  origin  of  social  order  ;  and  when 
in  the  third  state  the  people  settle  in  fixed  habitations,  the 
laws  gradually  assume  the  more  regular  form  of  a  monarchical 
or  republican  government.  Every  thing  now  wears  a  new 
aspect ;  industry  flourishes,  the  arts  are  invented,  the  use  of 
metals  is  discovered  ;  labour  is  subdivided ;  every  one  ap- 
plies himself  more  particularly  to  a  distinct  employment,  in 
which  he  becomes  skilful.  Thus,  by  slow  degrees,  this  peo- 
ple of  savages,  whose  origin  was  so  rude  and  miserable,  be- 
come a  civilized  people,  who  occupy  a  highly  cultivated 
country,  crossed  by  fine  roads,  leading  to  wealthy  and  popu- 
lous cities,  and  carrying  on  an  extensive  trade  with  other 
countries. 

The  whole  business  of  political  economy  is  to  study  the 
causes  which  have  thus  co-operated  to  enrich  and  civilize  a 
nation.  This  science,  therefore,  is  essentially  founded  upon 
history, — not  the  history  of  sovereigns,  of  wars,  and  of  in- 
trigues,— but  the  history  of  the  arts,  and  of  trade,  of  discove- 
ries, and  of  civilization.  We  see  some  countries,  like  Ame- 
rica, increase  rapidly  in  wealth  and  prosperity,  whilst  others, 
like  Egypt  and  Syria,  are  impoverished,  depopulated,  and 
fsvlling  to  decay  ;  when  the  causes  which  produce  these  va- 


i»RDPERTY.  23& 

rious  effects  are  well  understood,  some  judgment  may  be 
formed  of  the  measures  which  governments  have  adopted  to 
contribute  to  the  vvelfare  of  their  people  ;  whether  certain 
branches  of  commerce  should  be  encouraged  in  preference 
to  others  ;  whether  it  be  proper  to  prohibit  this  or  that  kind 
of  merchandise  ;  whether  any  peculiar  encouragement  should 
be  given  to  agriculture  ;  whether  it  be  right  to  establish  by 
law  the  price  of  provisions  or  the  price  of  labour,  or  whether 
they  should  be  left  without  control ;  and  whether  many  other 
measures,  which  influence  the  welfare  of  nations,  should  be 
adopted  or  rejected. 

It  is  manifest,  therefore,  that  political  economy  consists, 
of  two  parts — theory  and  practice ;  the  science  and  the  art. 
The  science  comprehends  a  knowledge  of  the  facts  which 
have  been  enumerated ;  the  art  relates  more  particularly  to 
legislation,  and  consists  in  doing  whatever  is  requisite  to  con- 
tribute to  the  increase  of  national  wealth,  and  avoiding  what- 
ever would  be  prejudicial  to  it.  Mrs.  Bryan. 

Questions. — 1.  What  is  political  economy  ?  2,  What  is  the  state 
of  savage  life  ?  3.  What  is  the  consequence  of  attending  to  pasturage  ? 
4.  What  is  the  effect  of  discovering  the  art  of  tillage  ?  5.  What  in? 
troduces  property  ?  6.  What  is  the  origin  of  social  order  ?  7.  What 
follows  after  the  laws  assume  the  regular  form  of  a  government?  8. 
On  what  is  the  science  of  political  economy  founded  ?  9.  How  may 
some  judgment  he  formed  of  the  measures  of  governments  ?  10.  What 
does  the  science  of  political  economy  comprehend  ?    11.  The  art  ? 


ILESSGN  105, 

Property. 

When  we  consider  the  multitude  who  are  in  possession  of 
means  of  enjoyment,  that  are  to  them  the  means  only  of  selfish 
avarice  or  of  profligate  waste,  and  when,  at  the  same  time,  we 
consider  the  multitudes,  far  more  numerous,  to  whom  a  small 
share  of  that  cumbrous  and  seemingly  unprofitable  wealth, 
would  in  an  instant  diffuse  a  comfort,  that  would  make  the 
heart  of  the  indigent  gay  in  his  miserable  hovel,  and  be  like 
a  dream  of  health  itself  to  that  pale  cheek,  which  is  slowly 
wasting  on  its  wretched  bed  of  straw,  in  cold  and  darkness, 
—-it  might  almost  seem  to  th^  inconsiderate,  at  least  for  a 


^36  PROPERTY. 

moment,  that  no  expression  of  the  social  voice  could  be  so 
beneficial,  as  that  which  should  merely  say,  let  there  be  no 
restraint  of  property,  but  let  all  the  means  of  provision  for 
the  wants  of  mankind,  be  distributed  according  to  the  more 
or  less  imperious  necessity  of  those  wants,  which  all  partake. 
It  requires  only  the  consideration  of  a  moment,  however,  to 
perceive,  that  the  very  distribution,  would,  itself,  be  the  most 
injurious  boon  that  could  be  offered  to  indigence, — that  soon, 
under  such  a  system  of  supposed  freedom  from  the  usurpa- 
tions of  the  wealthy,  there  would  only  be  one  general  penury, 
without  the  possibility  of  relief;  and  an  industry,  that  would 
be  exercised,  not  in  plundering  the  wealthy,  for  there  could 
not  then  be  wealth  to  admit  of  plunder,  but  in  snatching 
from  the  weaker  some  scanty  morsel  of  a  wretched  aliment, 
that  would  scarcely  be  sufficient  to  repay  the  labour  of  the 
struggle,  to  him  who  v/as  too  powerful  not  to  prevail.  There 
would  be  no  palaces,  indeed,  in  such  a  system  of  equal  ra- 
pine,— and  this  might  be  considered  as  but  a  slight  evil,  from 
the  small  number  of  those  who  were  stripped  of  them ;  but 
when  the  chambers  of  state  had  disappeared,  where  would 
be  the  cottage,  or  rather  the  whole  hamlet  of  cottages,  that 
might  be  expected  to  occupy  its  place  ?  The  simple  dwell- 
ings of  the  unhappy  peasant  might  be  the  last,  indeed,  to  be 
invaded  ;  but  when  the  magnificent  mansion  had  been  strip- 
ped by  the  first  band  of  plunderers-,  |hese  too  would  soon 
find  plunderers  as  rapacious.  No  elegant  art  could  be  ex- 
ercised, no  science  cultivated,  where  the  search  of  a  preca- 
rious existence  for  the  day,  would  afford  us  no  leisure  for 
studies  or  exercises  beyond  the  supply  of  mere  animal  wants  ; 
and  man,  who,  with  property,  is  what  we  now  behold  him, 
and  is  to  be,  in  his  glorious  progress  even  on  earth,  a  being 
far  nobler  than  we  are  capable,  in  our  present  circumstances^ 
of  divining, — would,  without  property,  soon  become,  in  the 
lowest  depth  of  brutal  ignorance  and  wretchedness,  what  it 
is  almost  as  difficult  for  our  imagination  to  picture  to  us,  aS 
it  would  be  for  it  to  picture  what  he  may  become  on  earthj 
after  the  many  long  ages  of  successive  improvement. 

The  great  inequality  of  property,  strange  as  it  may  seem 
to  be  at  any  one  moment,  is  only  the  effect  of  that  security 
and  absolute  command  of  property,  which  allows  the  con- 
tinual accumulation  of  it  by  continued  industry.  If  all 
things  had  been  common  to  all,— instead  of  that  beawtiful 


DIVISION   OF   LABOUR.  237 

and  populous  earth  which  we  behold, — where  cities  pour 
wealth  on  the  fields,  and  the  fields,  in  their  turn,  send  plenty 
to  the  cities, — where  all  are  conferring  aid  and  receiving 
aid,  and  the  most  sensual  and  selfish  cannot  consume  a  sin- 
gle luxury,  without  giving,  however  unintentionally,  some 
comfort,  or  the  means  of  comfort  to  others, — instead  of  this 
noble  dwelling-place  of  so  many  noble  inhabitants,  we  should 
have  had  a  waste  or  a  wilderness,  and  a  few  miserable  strag- 
glers, half  famished  on  that  wide  soil  which  now  gives  abun- 
dance to  millions.  Brown. 

Question. — What  reasons  may  be  given  for  the  institution  of  pro* 
perty  ? 


LESSON  106 

Division  of  Labour. 

Smelling,  the  melting  of  ore  in  a  furnace  so  as  to  extract  th« 
metal.     In  the  more  precious  metals  this  is  called  refining. 

That  separation  of  employments,  which,  in  political  eco- 
nomy, is  called  the  division  of  labour,  can  take  place  only  in 
civilized  countries.  In  the  flourishing  states  of  Europe  and 
America  we  find  men  not  only  exclusively  engaged  in  the 
exercise  of  one  particular  art,  but  that  art  subdivided  into 
numerous  branches,  each  of  which  forms  a  distinct  occupa- 
tion for  the  different  workmen.  Observe  the  accommoda- 
tion of  the  most  common  artificer  or  day-labourer  in  a  civiliz- 
ed and  thriving  country,  and  you  will  perceive  that  the  number 
of  people,  of  whose  industry  a  part,  though  but  a  small  part, 
has  been  employed  in  procuring  him  this  accommodation, 
exceeds  all  computation.  The  woollen  coat,  for  example, 
which  covers  the  labourer,  though  it  may  appear  coarse  and 
rough,  is  the  produce  of  the  joint  labour  of  a  great  number 
of  workmen.  The  shepherds,  the  sorter  of  the  wool,  the 
carder,  the  dyer,  the  spinner,  the  weaver,  the  fuller,  the 
dresser,  with  many  others,  must  all  join  their  different  arts  to 
complete  even  this  ordinary  production.  How  many  merchants 
and  carriers,  besides,  must  have  been  employed  in  transport- 
ing the  materials  from  some  of  those  workmen  to  others  who 
often  live  in  a  distant  part  of  the  country  !    How  much  com- 


ii38  DIVISION    OF   LABOUH. 

merce  and  navigation  in  particular,  how  many  ship-buil(ler;§, 
sailors,  sail-makers,  rope-makers,  must  have  been  employed, 
in  order  to  bring  together  the  different  drugs  made  use  of 
by  the  dyer,  which  often  come  from  the  remotest  corners  of 
the  world  !  What  a  variety  of  labour  too  is  necessary  in 
order  to  produce  the  tools  of  those  workmen  !  To  say  no- 
thing of  such  complicated  machines  as  the  ship  of  the  sailor, 
the  mill  of  the  fuller,  or  even  the  loom  of  the  weaver,  let  us 
consider  only  what  a  variety  of  labour  is  requisite  to  form  that 
very  simple  machine,  the  shears  with  which  the  shepherd 
clips  the  wool.  The  miner,  the  builder  of  the  furnace  for 
heating  the  ore,  the  burner  of  the  charcoal  to  be  made  use 
of  in  the  smelting  house,  the  brick-maker,  the  brick-layer, 
the  workmen  who  attend  the  furnace,  the  mill-wright,  the 
forger,  the  smith,  must  all  of  them  join  their  different  arts 
in  order  to  produce  them.  Were  we  to  examine,  in  the  same 
manner,  all  the  different  parts  of  his  dress  and  household 
furniture,  the  different  hands  employed  in  preparing  his  food, 
the  glass  window  which  lets  in  the  heat  and  the  light,  and 
keeps  out  the  wind  and  the  rain,  with  all  the  knowledge  and 
art  requisite  for  preparing  that  beautiful  and  happy  inven- 
tion, together  with  the  tools  of  all  the  different  workmen 
employed  in  producing  those  different  conveniences  ;  if  we 
examine  all  these  things,  and  consider  what  a  variety  of  la- 
bour is  employed  about  each  of  them,  we  shall  be  sensible, 
that  without  the  assistance  and  co-operation  of  many  thou- 
sands, the  very  humblest  person  in  a  civilized  country  could 
not  be  provided  for,  even  according  to  what  we  falsely  ima- 
gine the  easy  and  simple  manner  in  which  he  is  commonly 
accommodated.  Compared,  indeed,  with  the  more  extrava- 
gant luxury  of  the  great,  his  accommodation  must  no  doubt 
appear  extremely  simple  and  easy ;  and  yet  it  may  be  true, 
perhaps,  that  the  accommodation  of  an  European  prince  does 
not  always  so  much  exceed  that  of  an  industrious  and  frugal 
peasant,  as  the  accommodation  of  the  latter  exceeds  that  of 
many  an  African  king,  the  absolute  master  of  the  lives  and 
liberties  of  ten  thousand  naked  savages. 


AGRICULTURE.  S39 

LESSON  107. 
Agriculture, 

Agriculture  is  the  science  which  explains  the  means  of 
making  the  earth  produce,  in  plenty  and  perfection,  those 
vegetables  which  are  necessary  to  the  convenience  or  sub- 
sistence of  man.  Its  practice  demands  a  considerable  know- 
ledge of  the  relations  subsisting  between  the  most  important 
objects,  of  nature.  It  is  eminently  conducive  to  the  advan- 
tage of  those  engaged  in  it,  by  its  tendency  to  promote  their 
health,  and  to  cherish  in  them  a  manly  and  ingenuous  cha- 
racter. Every  improvement  made  in  the  art  must  be  consi- 
dered as  of  high  utility,  as  it  facilitates  the  subsistence  of  a 
greater  proportion  of  rational  and  moral  agents ;  or  if  we 
suppose  the  number  to  be  unincreased,  furnishes  them  with 
greater  opportunities  than  could  be  possessed  before,  of  ob- 
taining that  intellectual  and  moral  enjoyment,  which  is  the 
most  honourable  characteristic  of  their  nature.  The  strength 
of  nations  is  in  proportion  to  their  skilful  cultivation  of  the 
soil ;  and  their  independence  is  secured,  and  their  patriotism 
animated,  by  obtaining  from  their  native  spot  all  the  requi- 
sites for  easy  and  vigorous  subsistence.  Not  only  to  raise 
vegetables  for  the  use  of  man,  but  for  those  animals  also 
which  are  used  as  food,  is  obviously,  therefore,  part  of  the 
occupation  of  the  husbandman ;  and  to  assist  him  in  his 
operations,  other  animals  are  to  be  reared  and  fed  by  him, 
to  relieve  his  labours  by  their  strength  and  endurance  of  ex- 
ertion. In  cold,  and  comparatively  infertile  climates,  the 
services  of  these  creatures  are  particularly  important,  if  not 
absolutely  indispensable,  and  their  health  and  multiplication 
become,  therefore,  objects  of  great  and  unremitted  attention. 

Since  the  errors  of  ancient  husbandry  have  been  correct- 
ed, and  vulgar  superstitious  traditions  exploded,  agriculture 
has  been  gradually  improving.  A  solid  and  rational  system 
of  the  art  has  been  founded  upon  clear  and  intelligible  prin- 
ciples. The  application  of  natural  history  and  chemistry  to 
it  has  greatly  accelerated  its  improvements.  Inquiries  have 
been  made  into  the  causes  of  the  fertility  and  barrenness  of 
land,  the  food  and  nutriment  of  vegetables,  the  nature  of 
soils,  and  the  best  modes  of  meliorating  them  with  variouB 


240  COMMERCE. 

manures.  Foreign  seeds  have  been  introduced,  and  the 
methods  of  cultivation  adopted  from  the  nations  whence  they 
were  borrowed.  Tiie  intelligent  farmer,  profiting  by  the 
wider  diffusion  of  knowledge,  derives  assistance  from  the 
philosopher,  and  is  furnished  with  the  useful  principles  of 
every  art  in  the  least  degree  conducive  to  the  improvement 
and  success  of  his  occupations. 

Questions. — 1.  What  is  agriculture  ?  2.  What  does  the  practice 
demand  ?  3.  Why  is  it  advantageous  to  those  who  engage  in  it  ?  4. 
Why  must  every  improvement  in  the  art  be  considered  of  high  utili- 
ty ?  5.  What  is  said  of  agricuUure  with  regard  to  nations  ?  6.  What 
belongs  to  the  business  of  the  husbandman  besides  the  raising  of  vege- 
tables ?    7.  What  is  said  of  modern  improvements  in  agriculture  ? 


LESSON  108. 

Commerce  and  Manufactures. 

Cap'ital,  the  fund  or  stock  of  a  trading  company,  or  corporation ; 
the  stock  which  a  merchant  or  tradesman  einpluys  in  business 
on  his  own  account. 

Commerce  is  the  interchange  of  commodities,  or  the  dis- 
posal of  produce  of  any  kind  for  other  articles,  or  for  some 
representative  of  value  for  which  other  articles  can  be  pro- 
cured, with  a  view  of  making  a  profit  by  the  transaction. 
The  term  is  usually  restricted  to  the  mercantile  intercourse 
between  different  countries.  The  internal  dealings  between 
individuals  of  the  same  country,  either  for  the  supply  of  im- 
mediate consumption,  or  for  carrying  on  manufactures,  is 
more  commonly  denominated  trade. 

Those  who  engage  their  capitals  in  commerce  or  trade, 
act  as  agents  between  the  producers  and  the  consumers  of 
the  fruits  of  the  earth ;  they  purchase  them  of  the  former, 
and  sell  them  to  the  latter,  and  it  is  by  profits  on  the  sale 
that  capital  so  employed  yields  a  revenue  or  income.  Com- 
merce or  trade  increases  the  wealth  of  a  nation,  not  by  rais- 
ing produce,  like  agriculture,  nor  by  working  up  raw  mate- 
rials like  manufactures ;  but  it  gi/es  an  additional  value  to 
commodities  by  bringing  them  from  places  where  they  are 
plentiful  to  those  where  they  are  scarce :  and  by  providing 
the  means  for  their  more  extended  distribution,   both  th« 


MANUFACTURES.  241 

agricultural  and  manufacturing  cjasses  are  incited  to  greater 
industry.  Agriculture  never  arrives  at  any  considerable, 
much  less  at  its  highest,  degree  of  perfection,  where  it  is 
not  connected  with  trade,  that  is,  where  the  demand  for  the 
produce  is  not  increased  by  the  consumption  of  trading 
cities.  But  it  should  be  remembered  that  agriculture  is  the 
immediate  source  of  human  provision ;  that  trade  conduces 
to  the  production  of  provision  only  as  it  promotes  agricul- 
ture ;  and  that  the  whole  system  of  commerce,  vast  and 
various  as  it  is,  has  no  other  public  importance  than  its  sub- 
serviency to  this  end. 

Manufactures  are  the  arts  by  which  natural  productions 
are  brought  into  the  state  or  form  in  which  they  are  con- 
sumed or  used.  Tliey  require  in  general  great  expenses 
for  their  first  establishment,  costly  machines  for  shortening 
manual  labour,  and  money  and  credit  for  purchasing  mate- 
rials from  distant  countries.  There  is  not  a  single  manu- 
facture of  Great  Britain  which  does  not  require,  in  some 
part  of  its  process,  productions  from  the  different  parts  of 
the  globe;  it  requires,  therefore,  ships  and  a  friendly  inter- 
course with  foreign  nations,  to  transport  commodities  and 
exchange  productions.  They  would  not  be  a  manufacturing 
unless  they  were  a  commercial  nation. 

The  two  sciences  which  most  assist  the  manufacturer,  are 
mechanics  and  chemistry ; — the  one  for  building  mills, 
working  mines,  and  in  general  for  constructing  machines, 
either  to  shorten  the  labour  of  man  by  performing  it  in  less 
time,  or  to  perform  what  the  strength  of  man  alone  could 
not  accomplish ;  the  other  for  fusing  and  working  ores,  for 
dyeing  and  bleaching,  and  extracting  the  virtues  of  various 
substances  for  particular  occasions. 

It  is  more  common  to  see  merchants  and  manufacturers 
accumulate  large  and  rapid  fortunes  than  farmers.  They 
are  a  class  who  generally  employ  capital  upon  a  much  larger 
scale,  hence  their  riches  make  a  greater  show.  Yet,  upon 
the  whole,  trade  and  manufactures  do  not  yield  greater 
profits  than  agriculture.  It  must  be  observed  that  though  a 
farmer  does  not  so  frequently  and  rapidly  amass  wealth  as  a 
merchant,  yet  neither  is  he  so  often  ruined  The  risks  a 
man  encounters  in  trade  are  much  greater  than  in  farming. 
The  merchant  is  liable  to  severe  losses  arising  from  contin- 
gencies in  trade ;  he  must  have  therefore  a  chance  of  making 
2J 


242  MONEY. 

proportionally  j^i.  ter  promts.  The  chances  of  gain  must 
balance  the  chances  of  loss.  If  he  be  so  skilful  or  so  for- 
tunate as  to  make  more  than  his  average  share  of  gains,  he 
will  accumulate  wealth  with  greater  rapidity  than  a  farmer  ; 
but  should  either  a  deficiency  of  talents  or  of  fortunate  cir- 
cumstances occasion  an  uncommon  share  of  losses,  he  may 
become  a  bankrupt.  The  rate  of  profits,  therefore,  upon 
any  employment  of  capital  is  proportioned  to  the  risks  with 
which  it  is  attended ;  but  if  calculated  during  a  sufficient 
period  of  time,  and  upon  a  sufficient  number  of  instances  to 
afford  an  average,  these  different  modes  of  employing  capital 
will  be  found  to  yield  similar  profits.  It  is  thus  that  the  dis- 
tribution of  capital  to  the  several  branches  of  agriculture, 
commerce,  and  manufactures,  preserves  a  due  equilibrium, 
which,  though  it  may  be  accidentally  disturbed,  cannot, 
whilst  allowed  to  pursue  its  natural  course,  be  permanently 
deranged.  A  remarkably  abundant  harvest  may  occasional- 
ly raise  the  rate  of  agricultural  profits,  or  a  very  bad  season 
may  reduce  them  below  their  level.  The  opening  of  a  trade 
with  a  new  country,  or  the  breaking  out  of  a  v/ar  which  im- 
pedes foreign  commerce,  will  affect  the  profits  of  the  mer- 
chant :  but  these  accidents  disturb  the  equal  rate  of  profits, 
as  the  winds  disturb  the  sea ;  and  when  they  cease,  it  re- 
turns to  its  natural  level. 

Questions. — 1.  What  is  commerce?  2.  Trade?  3.  How  docH 
commerce  or  trade  increase  the  wealth  of  a  nation  ?  4.  To  what  end 
is  the  whole  system  of  commerce  subservient  ?  5.  What  are  manu- 
factures ?  G.  What  is  said  of  the  connexion  of  manufactures  with 
trade  ?  7.  How  do  the  sciences  of  mechanics  and  chemistry  assist 
the  manufacturer  ?  8.  What  is  said  of  the  profits  arising  from  agricul- 
ture, commerce,  and  manufactures  ? 


LESSON  109. 

Money. 

Spe'^cie,  gold  and  silver  coin,  distinguished  from  paper  moSeyf 

Gold  and  silver,  when  first  introduced  into  commerce 

were  probably  bartered   like  other  commodities,    by  bulk 

merely ;  but  shortly,  instead  of  being  given  loosely  by  bulk, 

•very  portion  was  weighed  in  scales,  but  weight  was  no  se- 


\ 
MONEY,  2^4^  \ 


tmiiy  against  mixing  gold  and  silver  with  base  metals.  To 
prevent  that  fraud,  pieces  of  gold  and  silver  are  impressed 
with  a  public  stamp,  vouching  both  the  purity  and  the  quan- 
tity ;  and  such  pieces  are  termed  coin.  This  was  an  im- 
provement in  commerce,  and  at  first,  probably,  deemed  com- 
plete. It  was  not  foreseen  that  these  metals  wear  by  much 
handling  in  the  course  of  circulation,  and  consequently,  that 
in  time  the  public  stamp  is  reduced  to  be  a  voucher  of  the 
purity  only,  not  of  the  quantity.  This  embarrassment  is 
remedied  by  the  use  of  paper  money ;  and  paper  money  is 
attended  with  another  advantage,  that  of  preventing  the  loss 
of  much  gold  and  silver  by  wearing. 

Before  the  invention  of  money,  men  were  much  at  a  loss 
how  to  estimate  the  value  of  their  property.  In  order  to  ex- 
press that  value  they  were  necessarily  obliged  to  compare  it 
to  something  else,  and  having  no  settled  standard,  they  would 
naturally  choose  objects  of  known  and  established  value. 
Accordingly  we  read  both  in  Scripture  and  in  the  ancient 
poets,  of  a  man's  property  being  worth  so  many  oxen  and  so 
many  flocks  and  herds.  ^\'^e  are  informed  that  even  at  the 
present  day  the  Calmuc  Tartars  reckon  the  value  of  a  coat 
of  mail  from  six  to  eight,  and  up  to  the  value  of  fifty  horses. 
In  civilized  countries  every  one  estimates  his  capital  by  the 
quantity  of  money  it  is  worth  ; — he  does  not  really  possess 
the  sum  in  money,  but  his  property,  whatever  be  its  nature 
or  kind,  is  equivalent  to  such  a  sum  of  money. 

It  is  common  to  imagine  that  the  more  money  a  country 
possesses,  the  more  affluent  is  its  condition.  And  that  is 
usually  the  case.  But  the  cause  is  often  mistaken  for  the 
effect.  A  great  quantity  of  money  is  necessary  to  circulate 
a  great  quantity  of  commodities.  Rich  flourishing  countries 
require  abundance  of  money,  and  possess  the  means  of 
obtaining  it ;  but  this  abundance  is  the  consequence,  not  the 
cause  of  their  wealth,  which  consists  in  the  commodities  cir- 
culated, rather  than  in  the  circulating  medium.  The  in- 
crease of  European  comforts,  of  affluence,  of  luxury,  is  at- 
tributed to  the  influx  of  the  treasures  of  the  new  world — and 
with  reason ;  but  those  treasures  are  the  sugar,  the  coffee, 
the  indigo,  and  other  articles,  which  America  exports,  to 
obtain  which  Europe  must  send  her  commodities  that  have 
been  produced  by  the  employment  of  their  people.  Gold 
and  silver,  though  they  have  greatly  excited  their  avari^ 


244  SHIP  BUILDING. 

and  ambitioD,  have  eventually  contributed  but  little  tostiinu* 
late  their  industry.  It  has  been  remarked  of  Spain,  that  the 
gold  and  silver  of  America,  instead  of  animating  the  country 
and  promoting  industry,  instead  of  giving  life  and  vigour  to 
the  whole  community,  by  the  increase  of  arts,  of  manufac- 
tures, and  of  commerce,  had  an  opposite  effect,  and  produced 
in  the  event  weakness,  poverty,  and  depopulation.  The 
wealth  which  proceeds  from  industry  resembles  the  copious 
yet  tranquil  stream,  which  passes  silent,  and  almost  invisible, 
enriches  the  whole  extent  of  country  through  which  it  flows ; 
but  the  treasures  of  the  new  world,  like  a  swelling  torrent, 
were  seen,  heard,  felt,  and  admired  ;  yet  their  first  opera- 
tion was  to  desolate  and  lay  waste  the  spot  on  which  they 
fell.  The  shock  was  sudden  ;  the  contrast  was  too  great. 
Spain  overflowed  with  specie,  whilst  other  nations  were 
comparatively  poor  in  the  extreme.  The  price  of  labour, 
of  provisions^  and  of  manufactures,  bore  proportion  to  the 
quantity  of  circulating  cash.  The  consequence  is  obvious ; 
in  the  poor  countries  industry  advanced;  in  the  more 
wealthy  it  declined. 

Questions. — 1,  What  is  probable  respecting  gold  and  silver  on 
their  first  introduction  ?  2.  Why  were  gold  and  silver  coined .''  3.  To 
what  is  the  public  stamp  in  time  reduced  ?  4.  What  is  the  advantage 
of  paper-money  ?  5.  How  did  men  estimate  the  value  of  their  proper- 
ty before  the  invention  of  money  ?  6.  How  is  capital  estimated  in 
civilized  countries  ?  7.  What  is  said  of  an  abundance  of  money  .'  8. 
What  baa  been  remarked  of  Spain  ? 


LESSON  110. 

Ship-building  and  Navigation. 

No  art  or  profession  has  appeared  more  astonishing  and 
marvellous  than  that  of  navigation,  in  the  state  in  which  it 
is  at  present.  This  cannot  be  made  more  evident  than  by 
taking  a  retrospective  view  of  the  tottering,  inartificial  craft 
to  which  navigation  owes  its  origin  :  and  by  comparing  them 
with  the  noble  and  majestic  edifices  now  in  use,  containing 
a  thousand  men,  with  thei'r  provisions,  drink,  furniture, 
wearing-apparel,  and  other  necessaries  for  many  months, 
besides  a  hundred  pieces  of  heavy  ordnance,  and  carrying 


NAVIGATION. 


245 


all  this  vast  apparatus  safely,  on  the  wings  of  the  wind, 
across  immense  seas. 

These  majestic  floating  structures  are  the  result  of  the 
ingenuity  and  united  labour  of  many  hundred  of  hands,  and 
are  composed  of  a  great  number  of  well-proportioned  pieces 
of  timber,  nicely  fastened  together  by  means  of  iron  nails 
and  bolts,  and  rendered  so  tight  with  tow  and  pitch,  that  no 
water  can  penetrate  into  any  part. 

To  give  motion  to  these  enormous  machines,  lofty  pieces 
of  timber  called  masts,  have  been  fixed  upright  in  them ; 
and  sails  of  linen  cloth  are  placed  for  the  purpose  of  catch- 
ing the  wind,  and  receiving  its  propelling  power.  It  has 
been  requisite  also  to  add  vast  quantities  of  cordage  and 
tackling.  Yet  all  these  would  be  insufficient  for  the  perfect 
government  and  direction  of  the  vessel,  if  there  were  not 
fastened  to  the  hinder  part  of  it,  by  means  of  hinges  and 
hooks,  a  moveable  piece  of  wood  called  the  rudder,  very 
small  in  proportion  to  the  whole  machine,  but  the  least  in- 
clination of  which  to  either  side  is  sufficient  to  give  imme- 
diately a  different  direction  to  the  enormous  mass  ;  so  that 
two  men  may  direct  and  govern  this  floating  town,  with  the 
same  or  with  greater  ease  than  a  single  man  can  direct  a 
boat. 

Even  the  vaulted  part  of  the  fabric,  together  with  its  sharp 
termination  underneath,  is  proportioned  according  to  the 
nicest  calculations  ;  and  the  length,  width,  and  strength  of 
the  sails  and  tackling,  are  all  in  due  proportion  to  one  ano- 
ther, according  to  certain  rules  founded  upon  the  principles 
of  the  art  of  ship-building. 

A  large  -ship  carries  at  least  2200  tons  burden,  that  is, 
'4,500,0001b.,  and  at  the  same  time  is  steered  and  governed 
with  as  much  ease  as  the  smallest  boat.  And  yet  if  such  a 
ship  sailed  along  the  coast  only,  and,  like  the  navigators  of 
old,  never  lost  sight  of  the  shore,  we  might  still  look  on 
navigation  as  an  easy  business.  But  to  find  the  shortest  way 
across  an  ocean  from  4000  to  6000  miles  in  width,  sailing  by 
day  or  by  night,  in  fair  weather  or  m  foul,  as  well  when  the 
sky  is  overcast,  as  vvhen  it  is  clear,  with  no  other  guide  than 
the  compass,  or  the  height  of  the  sun,  the  moon  and  stars, 
with  exactness  and  precision,  is  the  extraordinary  and  surpris- 
ing task  of  him  who  is  skilled  in  the  science  oi  n  vibration. 

A  violent  storm  of  wind  will  raaice  us  tremlie  'i  fear  ill 
21  * 


246  ARCHITECTURE. 

a  well-built  house,  in  the  midst  of  a  populous  city ;  but  the 
seaman,  provided  he  has  a  good  ship,  rides  with  unshaken 
courage,  amidst  the  enraged  waves,  when  the  whole  surface 
of  the  ocean  presents  to  the  eye  an  awful  scene  of  immense 
watery  mountains  and  bottomless  precipices. 


LESSON  111.  I 

Architecture.  1 

Amongst  the  various  arts  cultivated  in  society,  some  are  ^ 
only  adapted  to  supply  our  natural  wants  or  assist  our  in-  \ 
firmities ;  some  are  instruments  of  luxury  merely,  and  cal-  ) 
culated  to  flatter  our  pride,  or  gratify  our  desires  :  whilst  J 
others  tend  at  once  to  secure,  to  accommodate,  delight,  and  f. 
give  consequence  to  the  human  species. — Architecture  is  ] 
of  this  latter  kind  ;  and  when  viewed  in  its  full  extent,  may  j 
truly  be  said  to  have  a  very  considerable  part  in  almost  every  j 
comfort  or  luxury  of  life.  Houses  are  among  the  first  steps 
towards  civilization,  and  have  great  influence  both  on  the  \ 
body  and  mind.  Secluded  from  each  other,  and  inhabitants  ' 
of  woods,  of  caves,  or  of  wretched  huts,  men  are  generally 
indolent,  dull,  and  abject,  with  faculties  benumbed,  and  \ 
views  limited  to  the  gratification  of  their  most  pressing  ne-  ; 
cessities  ;  but  wherever  societies  are  formed,  and  commo- 
dious dwellings  are  found,  in  which,  well  sheltered,  they  \ 
may  breathe  a  temperate  air,  amid  the  summer's  heat  or  win-  ^ 
ter's  cold  ;  sleep  when  nature  calls,  at  ease  and  in  security  ; 
study  unmolested;  converse  and  taste  the  sweets  of  social  \ 
enjoyments ;  there  they  are  spirited,  active,  ingenious,  and  1 
enterprising  ;  vigorous  in  body,  speculative  in  mind ;  agri-  ■ 
culture  and  arts  improve  ;  the  necessaries,  the  conveniences,  | 
and  soon  even  the  luxuries  of  life  become  abundant.  | 

The  immediate  and  most  obvious  advantages  of  building  j 
are,  employing  many  ingenious  artificers,  many  industrious  | 
workmen,  and  labourers  of  various  kinds  ;  converting  ma-  ■ 
terials  of  little  value  into  the  most  stately  productions  of  | 
human  skill ;  beautifying  the  face  of  countries ;  and  multi-  f 
plying  the  comforts  of  life.  But  these,  however  great,  are 
n^t  the  most  considerable  :  that  numerous  train  of  arts  and 


ARCHITECTURE.  247 

manufactures,  contrived  to  furnish  and  adorn  the  works  of 
architecture,  which  occupies  thousands,  and  constitutes 
many  lucrative  branches  of  commerce ;  that  certain  con- 
course of  strangers,  to  every  country  celebrated  for  stately 
structures,  who  extend  your  fame,  and  create  a  demand  for 
your  productions,  are  considerations  of  the  highest  conse- 
quence.. Nor  is  architecture  less  useful  in  defending,  than 
prosperous  in  adorning  and  enriching  countries  ;  she  guards 
their  coasts  with  ships  of  war,  secures  their  boundaries, 
fortifies  their  cities,  and  by  a  variety  of  useful  construc- 
tions, controls  the  ambition  and  frustrates  the  attempts  of 
foreign  powers ;  curbs  the  insolence,  and  averts  the  danger, 
and  the  liorror  of  internal  commotions. 

Materials  in  architecture  are  like  words  in  phraseology. 
They  have  separately  but  little  power,  but  they  may  be  so 
arranged,  as  to  excite  ridicule,  disgust,  or  even  contempt ; 
yet  when  combined  with  skill,  and  expressed  with  energy, 
they  actuate  the  mind  with  unbounded  sway.  An  able 
writer  can  move  even  in  common  language,  and  the  master- 
ly disposition  of  a  skilful  artist,  will  dignify  the  meanest  ma- 
terials ;  while  the  weak  efforts  of  the  ignorant  render  the 
most  costly  materials  despicable.  To  such  the  compliment 
of  Apelles  may  justly  be  applied,  who,  on  seeing  the  pic- 
ture of  a  Venus  magnificently  attired,  said  to  the  operator, 
"  Friend,  though  thou  hast  not  been  able  to  make  her  fair, 
thou  hast  certainly  made  her  fine." 

The  five  orders  of  architecture  were  successively  invent- 
ed in  ancient  Greece  and  Italy  ;  they  are  called  the  Tuscan, 
the  Doric,  the  Ionic,  the  Gorinthian,  and  the  Composite  ; 
and  are  to  be  found  in  all  the  principal  buildings  of  the 
Christian  world.  The  Saxons  had  a  simple  style  of  archi- 
tecture, distinguished  by  semi-circular  arches  and  massive 
plain  columns.  The  Normans  too  invented  a  beautiful  style 
of  architecture,  called  the  Gothic  ;  distinguished  by  its  light- 
ness and  profuse  ornaments  ;  by  its  })ointed  arches,  and  by 
its  pillars,  carved  to  imitate  several  conjoined.  A  knowledge 
of  the  several  species  of  architecture  may  be  conveyed  more 
efliectuaily  by  engravings,  than  by  any  verbal  descriptions. 

QUESTIONS. — 1.  To  what  objects  are  the  arts  adapted  ?  2.  What 
M  man  in  a  state  of  seclusion?  3.  Of  society  ?  4.  Describe  the  ad- 
vantages of  architecture.  5.  Why  are  materials  in  architecture  hke 
words  in  phraseology  ?    6.  What  tir?  the  five  orders  of  architecture  ? 


248       CONSTITUTION  OF  THE  UNITED  STATES. 

LESSON  112. 

Constitution  of  the  United  States. 

As  all  the  youth  of  America  ought  to  be  well  acquainted 
with  the  constitution  of  the  country  in  which  they  live,  and 
to  which  they  must  be  subject,  it  will  be  proper  to  exhibit 
its  general  outlines. 

A  strong  sense  of  the  value  and  blessings  of  union  induc- 
ed the  people  at  a  very  early  period  to  institute  a  federal  go- 
vernment to  preserve  and  perpetuate  it.  They  formed  it 
almost  as  soon  as  they  had  a  political  existence;  (1778) 
nay,  at  a  time  when  their  habitations  were  in  flames,  when 
many  of  them  were  bleeding  in  the  field,  and  when  the  pro- 
gress of  hostility  and  desolation  left  little  room  for  those  calm 
and  mature  inquiries  and  reflections  which  must  ever  pre- 
cede the  formation  of  a  wise  and  well  balanced  government 
for  a  free  people.  It  is  not  to  be  wondered  at,  that  a  go- 
vernment instituted  in  times  so  inauspicious,  should,  on  ex- 
periment, have  been  found  greatly  deficient,  and  inadequate 
to  the  purpose  it  was  intended  to  answer.  The  people  per- 
ceived and  regretted  these  defects.  They  observed  the  dan- 
ger which  threatened  their  union,  and  more  remotely  their 
liberty  ;  and  being  persutlded  that  ample  security  for  both 
could  only  be  found  in  a  national  government  more  wisely 
framed,  deputies  from  the  several  states  met  in  convention 
at  Philadelphia  (1787,)  to  take  the  important  subject  into 
consideration.  In  the  mild  season  of  peace,  with  minds  un- 
occupied with  other  subjects,  they  passed  many  months  in 
cool  uninterrupted  and  daily  consultations  ;  and  finally,  with- 
out having  been  awed  by  power,  or  influenced  by  any  pas- 
sion except  love  for  their  country,  they  presented  and 
recommended  to  the  people  the  constitution  or  form  of  go- 
vernment produced  by  their  joint  and  very  unanimout 
councils. 

The  government  of  the  United  States  is  called  republican. 
It  is  a  representative  democracy.  All  power  resides  ulti- 
mately in  the  people ;  but  they  exercise  it  by  means  of  their 
representatives,  or  persons  chosen  by  them  for  that  purpose. 
All  the  departments  of  the  government  are  bound  to  conform 


CONSTITUTION    OF   THE    UNITED    STATES,  24^ 

to  the  provisions  of  the  constitution,  and  the  act  of  any  one 
of  them,  even  an  act  of  Congress,  if  contrary  thereto,  is  void. 

The  most  fundamental  article  in  every  form  of  government 
is  the  legislative  branch,  w^hich  has  the  power  of  making  all 
the  laws  and  regulations  to  which  the  whole  community  must 
be-  subject.  This,  in  the  United  States,  consists  of  a  senate 
and  house  of  representatives,  jointly  called  the  Congress^ 
which  must  be  assembled  at  least  once  every  year.  The 
senate  consists  of  two  members  from  each  of  the  separate 
states,  chosen  by  the  legislatures  of  each  state  to  serve  foi* 
six  years.  The  seats  of  one  third  of  the  senators  are  vacated 
ever^  two  years.  The  senate  tries  all  persons  impeached  by 
the  house  of  representatives  ;  but  they  can  only  punish  by 
deprivation  of  office,  or  disqualification  in  future  ;  and  the 
conviction  must  be  by  the  votes  of  two  thirds  of  the  mem- 
bers present  at  any  trial.  The  Vice-president  presides  in 
the  senate,  but  without  a  vote,  except  in  case  of  an  equal  di- 
vision of  the  votes  of  the  other  members.  No  person  can 
be  a  senator  who  has  not  attained  to  the  age  of  thirty  years. 

The  members  of  the  house  of  representatives  must  be 
twenty-five  years  of  age,  and  they  are  chosen  by  tlie  people 
at  large  every  two  years.  The  number  of  the  representative 
body  varies  according  to  the  number  of  the  separate  states, 
and  the  population  of  each  state.  For  this  purpose  an  enu- 
meration of  all  the  people  must  be  made  every  ten  years, 
and  the  number  of  representatives  must  never  exceed  one 
for  every  thirty  thousand,  but  each  state  shall  have  at  least 
one  representative.  The  senators  and  representatives  re- 
ceive a  compensation  for  their  services,  to  be  ascertained  by 
law,  and  paid  out  of  the  treasury  of  the  United  States.  All 
bills  for  raising  revenue  must  originate  in  the  house  of  re- 
presentatives ;  but  the  senate  may  propose  or  concur  with 
amendments  as  on  other  bills. 

The  judicial  power  is  vested  by  the  constitution  in  a  su- 
preme court,  and  such  inferior  courts  as  Congress  shall  from 
time  to  time  appoint ;  and  all  the  judges  hold  their  office 
during  good  behaviour.  Besides  the  ordinary  exercise  of  its 
power  of  deciding  controversies,  it  is  incident  to  the  judicial 
power  of  the  United  States  to  pass  upon  the  acts  of  Congress 
and  decide  upon  their  constitutionality  ;  a  power  essential 
to  the  rights  of  the  people,  but  not  known  in  any  of  the  go- 
vernments of  Europe. 


S50  CONSTITUTION    OF   THE    UNITED    STATES. 

The  executive  power  is  vested  in  a  President,  who  is  cho" 
sen  every  fourth  year  by  electors  appointed  in  the  methods 
prescribed  by  the  constitutions  or  legislatures  of  the  separate 
states.  If  no  person  have  a  majority  of  the  votes  of  the  elec- 
tors, then  from  the  persons  having  the  highest  numbers  not 
exceeding  three  on  the  list  of  those  voted  for,  the  house  of 
representatives  shall  choose  the  president  by  ballot.  But  in 
choosing  the  president,  the  votes  must  be  taken  by  states, 
the  representatives  from  each  state  having  one  vote.  If  no 
person  have  a  majority  of  the  votes  of  the  whole  number  of 
electors  for  vice-president,  then  from  the  two  highest  num- 
bers on  the  list,  the  senate  shall  choose  the  vice-president. 

The  president  must  be  thirty-five  years  of  age,  and  he 
may  be  re-elected  as  often  as  the  people  please.  He  is  liable 
to  be  impeached  and  removed  from  office  for  misbehaviour. 
He  is  the  commander  in  chief  of  the  army  and  navy  :  and 
by  and  with  the  advice  and  consent  of  the  senate,  makes 
treaties,  appoints  judges,  foreign  ministers,  and  other  officers. 
If  the  president  disapprove  of  any  bil*'  presented  to  him,  after 
having  had  the  concurrence  of  both  houses,  he  must  give 
his  objections  to  it ;  and  if  two  thirds  of  each  house  still 
abide  by  their  first  vote,  the  bill  passes  into  a  law,  notwith- 
standing his  rejection  of  it. 

Besides  the  general  government,  whose  power  for  many 
purposes  extends  over  the  whole  union,  each  state  has  a  se- 
parate local  government,  whose  jurisdiction  is  confined  to 
the  regulation  of  its  own  concerns.  These  separate  govern- 
ments are  all  republican,  and  consist  generally  of  a  governor, 
and  two  legislative  branches,  though  the  powers  of  the  diffe- 
rent departments  are  variously  modelled  in  the  several  states. 

Questions. — 1.  When  did  the  people  of  the  United  States  first 
form  a  government  ?  2.  What  served  to  render  this  government  de- 
ficient ?  3.  When  did  a  convention  meet  to  form  our  present  consti- 
tution ?  4.  Under  what  advantages  did  the  members  deliberate  ?  5. 
How  do  the  people  of  the  United  States  exercise  their  power  .^  6. 
What  power  has  the  legislative  branch  of  government  ?  7.  Of  what 
does  this  consist  in  the  United  States  ?  8.  Describe  the  senate.  9. 
House  of  representatives.  10.  Where  is  the  judicial  power  vested  ? 
11.  The  executive  ?  12.  Describe  the  manner  of  choosing  the  pre- 
sident and  vice-president.  13.  What  are  some  of  the  powers  which 
the  constitution  gives  the  president  ?  14.  What  is  said  of  the  go- 
vernments of  the  separate  states  ?  [Note.  The  principal  subordinate 
officers  in  the  executive  department,  are  the  secretaries  of  state,  of  tha 
treasury,  of  war,  and  of  the  navy.] 


EXCELLENCE  OP  OUR  REPUBLICAN  GOVERNMENT.  251 

LESSON  113. 

^Excellence  of  our  Republican  Government 

■*• 

fiT  is  the  just  pride  of  the  peopie  of  the  United  States^ 
at  they  have  attempted  a  mode  of  government  which  di- 
vests itself  of  all  the  support  which  is  derived  from  the  ho- 
nest weaknesses  and  attachments  of  the  human  mind  ;  which, 
disclaiming  all  alliance  with  reverence  of  ancient  authority, 
or  the  deep-rooted  habits  of  unthinking  obedience,  trusts 
itself,  with  no  other  attractions  than  its  own  moral  worth  and 
dignity,  to  the  custody  of  our  virtues.  By  subjecting  legis- 
lative bodies  to  rule,  and  holding  them  under  the  restraints 
of  those  fundamental  principles  and  enactments,  which  we 
call  the  constitution,  we  have  given  a  new  dignity  and  a 
higher  duty  to  law,  and  realized  the  noble  idea  of  a  moral 
supremacy,  clothed  with  power,  to  hold  not  only  subjects  of 
the  government  to  a  just  performance  of  their  various  indi- 
vidual duties,  but  also  the  government  itself,  in  all  its  depart 
ments,  in  its  proper  place  and  sphere. 

In  the  brighter  moments  of  our  hopes  for  the  future  for- 
tunes of  our  country,  we  may  exclaim  with  Sir  William 
Jones — 

What  constitutes  a  state  1 
Not  high  raised  battlement  or  laboured  mound, 

Thick  wall  or  moated  gate  ; 
Not  cities  proud,  with  spires  and  turrets  crowned  ; 

Not  bays  and  broad  armed  ports, 
Where  laughing  at  the  storm  rich  navies  ride ; 

Not  starred  and  spangled  courts, 
Where  low  browed  baseness  wafts  perfume  to  pride. 

No  !  Men,  high  minded  men, 
With  powers  as  far  above  dull  brutes  endued, 

In  forest,  brake,  or  den. 
As  beasts  excel  cold  rocks  and  brambles  rude ; 

Men,  who  their  duties  know, 
But  know  their  rights,  and  knowing,  dare  maintain, 

Prevent  the  long  aimed  blow, 
And  crush  the  tyrant  while  they  rend  the  chain  : 

These  constitute  a  state  ; 


ii52  INTELLIGENCE    OP    THE    PEOPLE. 

And  sovereign  Imo,  that  state's  collected  will, 

O'er  thrones  and  globes  elate, 
Sits  empress,  crowning  good,  repressing  ill. 

We  may  be  told  that  this  is  gt  vision  of  a  perfect  common- 
wealth ;  and  so  it  is  : — still  the  hopes  of  patriots  and  sages, 
amid  discouragement  and  defeat,  gather  about  and  rest  upon 
it,  with  something  of  that  gladness  of  heart,  which  the  tired 
traveller  feels,  when  he  hrst  descries  the  sun  light  upon  the 
distant  towers  of  the  happy  valley. 

Although  the  dangers  of  American  liberty  may  arise  and 
press  upon  us  from  every  side,  to  chastise  our  hopes  and  our 
confidence,  the  duty  of  its  friends  is  not  doubtful.  They 
must  labour  to  augment  that  moral  force,  to  which  its  very 
existence  is  committed.  N.  Am.  Review. 


LESSON  114.  1 

Intelligence  of  the  People  a  means  of  safety  to  the  Govern^   j 
ment.  mt.  rf. 

In  a  government  like  ours,  where  the  supreme  control    | 
depends  on  the  opinion  of  the  people,  it  is  important  certainly    i 
that  this  opinion  should  be    enlightened.      "  There  is  no    1 
power  on  earth  which  sets  ap  its  throne  in  the  spirit  and  V 
souls  of  men,  and  in  their  hearts  and   imaginations,  their    \ 
assent  also  and  belief^  equal  to  learning  and  knowledge  ;  and    j 
there  is  scarce  one  instance  brought  of  a  disastrous  govern-    • 
ment,  where  learne  i  men   have  been  seated  at  the  helm." 
Now  the  most  certain  mode  of  making  learned  rulers,  is  to 
extend  as  far  as  possible  the   influence  of  learning  to  the 
people  from  whom  the  rulers  are  taken.     But  intelligence 
not  only  makes  good  rulers,  it  makes  peaceable  citizens.    It 
causes  men  to  have  just  views  of  the  nature,  value,  and  re- 
lations of  things,  the  purposes  of  life,  the  tendency  of  actions, 
to  be  guided  by  purer  motives,  to  form   nobler  resolutions, 
and  press  forward  to  more  desirable  attainments.     Laws  will 
be  obeyed,  because  they  are  understcod  and  rightly  estimat- 
ed.    Men  will  submit  cheerfully  to  good  government,  and 
fionsult  the  peace  of  society,  in  proportion  as  they  learn  to 


INTELLIGENCE  OP  THE  PEOPLE.  253 

respect  themselves,  and  value  their  own  character.  These 
things  are  the  fruit  of  knowledge.  But  ignorance  is  a  soil 
which  gives  exuberant  growth  to  discords,  delusions,  and  the 
dark  treacheries  of  faction.  While  the  people  are  ignorant, 
they  are  perpetually  subject  to  false  alarms,  and  violent  pre- 
judices, ready  to  give  a  loose  rein  to  the  wild  storms  of  their 
passions,  and  prepared  to  yield  themselves  willing  victims  to 
the  seductions  of  every  ambitious,  turbulent,  treacherous, 
and  faithless  spirit,  who  may  choose  to  enlist  them  in  his 
cause.  Knowledge  will  work  upon  this  charm  with  a  potent 
efficacy,  lay  the  hideous  spectres  which  it  calls  up,  and  pre- 
serve the  soundness  and  growing  strength  of  the  social  and 
political  fabric. 

It  should  be  considered  the  glory,  and  the  duty  of  the  go- 
vernment, to  aid  in  establishing  morals  and  religion.  The" 
first  step  in  accomplishing  this  purpose  is  to  fix  the  princi- 
ples of  virtue,  and  impress  the  importance  of  religious  prac- 
tice, by  enlarging  the  sphere  of  mental  light,  touching  the 
springs  of  curiosity,  opening  the  channels  of  inquiry,  and 
pouring  into  the  mind  new  materials  of  thought  and  reflec- 
tion. All  branches  of  intellectual  improvement  will  lead  to 
moral  goodness.  The  mind,  which  is  taught  to  expatiate 
throughout  the  works  of  God,  to  ascend  to  the  heavenly 
worlds  and  find  him  there,  to  go  into  the  deep  secrets  of  na- 
ture and  find  him  there,  to  examine  the  wonders  of  its  own 
structure,  and  look  abroad  into  the  moral  constitution  of 
things,  and  perceive  the  hand  of  an  invisible.  Almighty  Be- 
ing, giving  laws  to  the  whole,  will  be  impressed  v/ith  a  sense 
of  its  own  dependence,  and  feel  something  of  the  kindling 
flame  of  devotion.  It  is  not  in  human  nature  to  resist  it. 
And  so  the  man  who  begins  to  study  the  organization  of  so- 
ciety, the  mutual  relations  and  dependencies  of  its  parts,  its 
objects,  and  the  duties  it  imposes  on  those  who  enjoy  its  be- 
nefits, will  soon  be  made  to  respect  its  institutions,  value  its 
privileges,  and  practise  the  moral  virtues,  in  which  its  very 
existence  consists.  The  more  extensively  these  inquiries 
are  encouraged,  and  these  principles  indicated,  in  the 
elements  of  education,  the  greater  will  be  the  certainty  of 
moral  elevation  of  character,  and  the  brighter  the  prospects 
of  a  virtuous  community.  In  regard  to  religion,  ignorance 
is  its.  deadliest  bane.  It  gathers  the  clouds  of  prejudice  from- 
ajl  the  dark  corners  of  the  mind,  and  causes  them  to  brood 
22 


25#  THE  GOVERNMENT  OF  ENGLAND. 

over  the  itnderstanding,  and  too  often  the  heart,  with  a  dis- 
mal, chilling  influence.  It  gives  perpetuity  to  error,  defies 
the  weapons  of  argument  and  reason,  and  is  impassive  even 
to  the  keen  sword  of  eternal  truth.  To  bring  into  salutary 
action  these  two  great  instruments  of  human  happiness,  mo- 
rals and  religion,  nothing  is  of  so  much  importance,  as  to 
multiply  the  facilities  of  education,  and  quicken  the  spirit  of 
enlightened  inquiry. 

Through  the  medium  of  education  the  government  may 
give  a  stronger  impulse  to  the  arts,  and  help  to  build  up  the 
empire  of  the  sciences.  Before  men  can  invent,  or  make 
profound  discoveries,  they  must  be  taught  to  think.  Savages 
never  advance  a  step  Hirther  in  inventions  and  discoveries, 
than  they  are  compelled  by  their  wants.  The  external  com- 
forts of  civilized  life  depend  on  tlife  useful  arts,  which  an 
improved  state  of  the  intellect  has  brought  to  light.  In  the 
sciences,  and  in  literature,  we  have  a  vast  uncultivated  field 
before  us.  In  the  arts  of  traffic,  and  the  mysteries  of  gain, 
we  may  perhaps  be  contented  with  the  skill  we  possess. 
But  to  be  contented  with  our  progress  in  the  sciences  and 
literature,  and  all  tho.se  attainments,  which  chiefly  dignify 
and  adorn  human  nature,  would  argue .  an  obtuseness  and 
apathy  altogether  unworthy  of  a  people,  who  are  blessed  with 
so  many  political,  civil,  and  local  advantages  of  various  kinds, 
as  the  inhabitants  of  the  United  States. 

North  American  Review. 

Questions. — 1.  What  are  some  of  the  advantages  of  knowledge 
with  regard  to  rulers  and  the  people  ?  2.  What  are  some  of  the  ef- 
fects of  ignorance  ?  3.  How  may  government  aid  in  establishing 
morals  and  religion  ?  4.  How  does  intellectual  improvement  promote 
devotional  feelings  ?  5.  What  will  be  the  effect  of  studying  the  or- 
ganization of  society  ?  6.  What  is  the  effect  of  ignorance  in  regard 
to  religion  ? 


LESSON  115. 

The  Government  of  England. 

The  government  of  England,  which  has  sometimes  been 
called  a  mixed  government,  sometimes  a  limited  monarchy, 
iis  formed  by  a  combination  of  the  three  regular  species  of 


THE  GOVERNMENT'  OF  ENGLAND.  255 

government ;  the  monarchy,  residing  in  the  king  •  the  aris- 
tocracy in  the  house  of  lords  ;  and  the  republic  being  repre- 
sented by  the  house  of  commons.  The  crown  of  the  united 
kingdom  of  Great  Britain  and  Ireland  is  hereditary,  and  its 
rightful  inheritor  is  bound,  by  the  cotiditions  of  his  inheri- 
tance, to  the  discharge  of  certain  duties,  as  well  as  vested 
with  certain  povvers  and  privileges.  By  the  oath  adminis- 
tered to  the  sovereign  at  his  coronation,  he  solemnly  engages 
to  govern  according  to  law,  to  execute  judgment  in  mercy, 
and  to  maintain  the  established  religion.  To  the  king  be- 
longs the  sole  power  of  sending  and  receiving  ambassadors ; 
and  it  is  his  prerogative  also  to  enter  into  treaties,  and  to 
form  alliances  with  foreign  princes  and  states,  to  make  war 
or  peace,  to  raise  and  regulate  fleets  and  armies,  to  erect 
fortifications,  to  coin  money,  to  regulate  commerce,  and  to 
establish  courts  of  judicature.  He  is  the  fountain  of  honour, 
office,  and  privilege,  and  he  can  grant  letters  of  nobility  and 
erect  corporations.  The  king  has  an  absolute  negative  upon 
the  acts  of  parliament,  his  person  is  sacred,  and  he  is  not 
accountable  for  misconduct.  It  is  a  principle  of  the  consti- 
tutional law  that  "  the  king  can  do  no  wrong  ;"  but  it  is  pro- 
vided, that  for  all  his  public  acts,  his  ministers  and  advisers 
are  responsible  to  the  nation  at  large  by  the  medium  of  the 
parliament,  and  other  legally  constituted  assemblies. 

The  house  of  peers  is  composed  of  the  lords  spiritual  and 
the  lords  temporal.  The  former  consist  of  two  archbishops, 
and  twenty- four  bishops,  who  are  a  kind  of  representatives 
of  the  clergy  of  England  and  Wales  ;  and  of  four  b'shops, 
who  are  taken  by  rotation  from  the  eighteen  bishops  of  Ire- 
land. With  regard  to  England  the  number  of  temporal 
peers  is  unlimited.  The  Scotch  peers  are  sixteen  in  num- 
ber, and  are  elected  by  their  own  body  for  one  parliament 
only.  The  lords  temporal  are  divided  into  dukes,  marquises, 
earls,  viscounts,  and  barons,  who  hold  their  respective  ranks 
in  the  foregoing  order,  by  hereditary  descent  or  by  creation. 
In  its  aggregate  capacity,  the  house  of  peers  has  a  right  to  a 
negative  upon  all  legislative  proposals. 

The  representatives,  who  constitute  the  hpuse  of  com- 
mons, or  the  lower  house  of  parliament,  are  divided  into  two 
classes,  knights  of  the  shire,  or  representatives  of  counties  ; 
and  citizens  and  burgesses,  or  representa-tives  of  cities  and 
boroughs.     The  qualification  for  voting  for  county  members, 


$2£^  THE  GOVERNMENT  OF  ENGLAND. 

is  the  possession  of  a  freehold  of  the  value  of  forty  shillings 
per  annum  or  upwards.  The  right  of  election  in  boroughs 
is  various,  depending  upon  the  charters  or  immemorial  usage 
of  each  place,  or  upon  decisions  made  by  committees  ap- 
pointed by  the  house  of  commons.  "There  is  nothing  in 
the  British  constitution  so  remarkable,"  says  Paley,  "  as  the 
irregularity  of  the  popular  representation.  If  my  estate  be 
situated  in  one  county  of  the  kingdom,  I  possess  the  ten 
thousandth  part  of  a  single  representative  ;  if  in  another, 
the  thousandth ;  if  in  a  particular  district,  I  may  be  one  in 
twenty  who  choose  two  representatives ;  if  in  a  still  more 
favoured  spot,  I  may  enjoy  the  right  of  appointing  two  my- 
self To  describe  the  staie  of  national  representation  as  it 
exists,  in  reality,  it  may  be  affirmed,  I  believe  with  truth, 
that  about  one  half  of  the  house  of  commons  obtain  their 
seats  by  the  election  of  the  people,  the  other  half  by  pur- 
chase, or  by  the  nomination  of  single  proprietors  of  great 
estates."  He  acknowledges  this  to  be  a  flagrant  incongrui- 
ty in  the  constitution  ;  but  he  doubts  whether  any  new 
scheme  of  representation  would  collect  together  more  wis- 
dom, or  produce  firmer  integrity.  The  house  of  commons 
enjoys  the  privilege  of  a  negative  upon  all  the  laws  which 
may  be  proposed  for  its  consideration,  and  exercises  the 
right  of  originating  all  bills,  which  levy  money  upon  the 
subject  by  way  of  taxes  or  assessments.  The  English  regard 
this  as  the  principal  safeguard  of  their  liberties,  and  the 
main  barrier  against  the  inordinate  increase  of  the  power  of 
the  crown,  for  the  commons  can  at  any  time  check  measures 
of  folly  or  guilt,  by  withholding  the  supplies,  and  without 
money  the  strength  of  the  executive  is  paralyzed.  The  king, 
however,  is  invested  with  a  power  to  dissolve  the  parliament, 
and  thus,  by  submitting  their  conduct  to  the  revision  of  their 
constituents,  to  appeal  against  them  to  the  nation  at  lar^O. 

Questions. — 1.  How  is  the  government  of  England  formed?  2. 
What  is  the  import  of  the  oath  which  the  king  lakes  at  his  coronation? 
3.  What  are  some  of  the  prerogatives  of  the  king?  4.  Describe  the 
house  of  peers.  5.  House  of  commons  ?  6.  What  are  the  remarks 
of  Paley  respecting  the  house  of  commons  ?  7.  What  do  tho  English 
legard  as  the  principal  safeguard  of  their  liberties  ? 


i 


AMERICA.  257 

LESSON  116. 

America. 

Here  the  free  spirit  of  mankind  at  length 
Throws  its  last  fetters  off;  and  who  shall  place 
A  limit  to  the  giant's  unchained  strength, 
Or  cilrb  his  swiftness  in  the  forward  race. 
For,  like  the  comet's  way  through  infinite  space, 
Stretches  the  long  untravell'd  path  of  light 
Into  the  depths  of  ages  :  we  may  trace, 
Afar,  the  brightening  glory  of  its  flight, 
Till  the  receding  rays  are  lost  to  human  sight. 

Europe  is  given  a  prey  to  sterner  fates. 
And  writhes  in  shackles  ;  strong  the  arms  that  chain 
To  earth  her  struggling  multitude  of  states  ; 
She  too  is  strong,  and  might  not  chafe  in  vain 
Against  them,  but  sliake  off*  the  vampyre  train 
That  batten  on  her  blood,  and  break  their  net. 
Yes,  she  shall  look  on  brighter  days,  and  gain 
The  meed  of  worthier  deeds ;  the  moment  set 
To  rescue  and  raise  up,  draws  near — but  is  not  yet. 

But  thou,  my  country,  thou  shalt  never  fall, 
But  with  thy  children — thy  maternal  care, 
Thy  lavish  love,  thy  blessings  shower'd  on  all — 
These  are  thy  fetters — seas  and  stormy  air 
Are  the  wide  barrier  of  thy  borders,  where 
Among  thy  gallant  sons  that  guard  thee  well, 
Thou  laugh'st  at  enemies  :  who  shall  then  declare 
The  date  of  thy  deep-founded  strength,  or  tell 
How  happy,  in  thy  lap,  the  sons  of  men  shall  dwell. 

Bryant 
22* 


256 


STRUCTURE    OF    THE    HUMAN    BODY. 


LESSON  117. 

Structui'c  of  the  Human  Body. 

Car'tilage,  gristle.     Ad'ipose,  fatty- 

Ten'dons,  hard,  insensible  cords,'  by  means  of  which  muscular 
fibres  are  attached  to  bone«. 

Dr.  Hunter  gives  the  following  beautiful  representation 
of  the  structure  of  the  human  body,  with  reference  to  all  the 
wants  and  requisites  of  such  a  being-  as  man,  in  answer  to  a 
supposed  objector,  who  asks  why  a  more  simple,  less  deli- 
cate, and  less  expansive  frame  had  not  been  adoj)ted.  First, 
says  he,  the  mind,  the  thinking,  immaterial  agent,  must  be 
provided  with  a  place  of  immediate  residence,  which  shall 
have  all  the  requisites  for  the  union  of  spirit  and  body  ;  ac- 
cordingly, she  is  provided  with  the  brain,  where  she  dwells 
as  governor  and  superintendent  of  the  whole  fabric.  In  the 
next  place,  as  she  is  to  hold  a  correspondence  with  all  the 
material  beings  around  her,  she  must  be  supplied  with  or- 
gans fitted  to  receive  the  different  kinds  of  impression  which 
they  will  make.  In  fact,  therefore,  we  see  that  she  is  pro- 
vided with  the  organs  of  sense,  as  we  call  them ;  the  eye  is 
adapted  to  light ;  the  ear  to  sound  ;  the  nose  to  smell ;  the 
mouth  to  taste  ;  and  the  skin  to  touch.  Further,  she  must 
be  furnished  with  organs  of  communication  betw  een  herself 
in  the  brain,  and  those  organs  of  sense  ;  to  give  her  infor- 
mation of  all  the  impressions  that  are  made  upon  them  ;  and 
ahe  must  have  organs  between  herself  in  the  brain,  and 
every  other  part  of  the  body  fitted  to  convey  her  commands 
and  influence  over  the  whole.  For  these  purposes  the  nerves 
are  actually  given.  They  are  soft  white  chords  which  rise 
from  the  brain,  the  immediate  residence  of  the  mind,  and 
disperse  themselves,  in  branches,  through  all  parts  of  the 
body.  They  convey  all  the  different  kinds  of  sensations  to 
the  mind  in  the  brain  ;  and  likewise  carry  out  of  thence  all 
her  commands  to  the  other  parts  of  the  body.  They  are  in- 
teamed  to  be  occasional  monitors  against  all  such  impressions 
as  might  endanger  tlie  well-being  of  the  whole,  or  of  any 
particular  port ;  which  vindicates  the  Creator  of  all  things, 
in  having  actually  subjected  us  to  those  many  disagreeable 
and  painful  sensations  which  we  are  exposed  to  from  a  thou- 
sand accidents  in  life. 


STRUCTURE  OF  tH£  HUMAN  BODY.        250 

The  mind,  in  this  corporeal  system,  must  be  endued  with 
the  power  of  moving  from  place  to  place  ;  that  she  may  have 
intercourse  with  a  variety  of  objects ;  that  she  may  fly  from 
such  as  are  disagreeable,  dangerous,  or  hurtful ;  and  pursue 
such  as  are  pleasant  and  useful  to  her.  And  accordingly  she 
is  furnished  with  limbs,  with  muscles  and  tendons,  the  instru- 
ments of  motion,  which  are  found  in  every  part  of  the  fabric 
where  motion  is  necessary.  But  to  support,  to  give  firmness 
and  shape  to  the  fabric  ;  to  keep  the  softer  parts  in  their 
proper  places ;  to  give  fixed  points  for,  and  the  proper  di- 
rections to,  its  motions,  as  well  as  to  protect  some  of  the  more 
important  and  tender  organs  from  external  injuries,  there 
must  be  some  firm  prop-work  interwoven  through  the  whole. 
And,  in  fact,  for  such  purposes  the  bones  are  given.  The 
prop-work  is  not  made  with  one  rigid  fabric,  for  that  would 
prevent  motion.  Therefore  there  are  a  number  of  bones. 
These  pieces  must  all  be  firmly  bound  together,  to  prevent 
their  dislocation.  And  this  end  is  perfectly  well  answered 
by  the  ligaments.  The  extremities  of  these  bony  pieces, 
where  they  move  and  rub  one  upon  another,  must  have 
smooth  and  slippery  surfaces  for  easy  motion.  This  is  most 
happily  provided  for,  by  the  cartilages  and  mucus  of  the 
joints.  The  interstices  of  all  these  parts  must  be  filled  up 
with  some  soft  and  ductile  matter,  which  shall  keep  them  in 
their  places,  unite  them,  and  at  the  same  time  allow  them 
to  move  a  little  upon  one  another  ;  these  purposes  are  an- 
swered by  the  cellular  membrane,  or  adipose  substance. 
There  must  be  an  outward  covering  over  the  whole  appara- 
tus, both  to  give  it  compactness,  and  to  defend  it  from  a 
thousand  injuries ;  which,  in  fact,  are  the  very  purposes  of 
the  skin  and  other  integuments. 

Questions. — 1.  How  does  the  soul  correspond  with  material  be- 
ings ?  2.  What  are  the  nerves,  and  their  use  ?  3.  Of  what  use  are 
tlie  bones  ?  4.  The  ligaments,  cartilages,  and  mucus  ?  5.  Cellular 
membrane  ?    6.  Skin  and  other  integuments  ? 


260  STRUCTURE    OF   THE    HUMAN   BODY. 


LESSON  118. 

Structure  of  the  Human  Body  (continued.) 

Socre'tion,   the  process  by  which   various  fluids  are  separate 
from  the  blood  by  means  of  the  glands.     Vas'cular,  full  of  ves- 
sels. 

The  mind  being  formed  for  society  and  intercourse  with 
beings  of  her  own  kind,  she  must  be  endued  with  powers  of 
expressing  and  communicating  her  thoughts  by  some  sensi- 
ble marks  or  signs,  which  sh;ill  be  both  easy  to  herself,  and 
admit  of  great  variety  ;  and  accordingly  she  is  provided  with 
the  organs  and  the  faculty  of  speech,  by  which  she  can  throw 
out  signs  with  amazing  facility,  and  vary  them  without  end. 
Thus  we  have  built  up  an  animal  body  which  would  seem 
to  be  pretty  complete ;  but  as  it  is  the  nature  of  matter  to  be 
altered  and  worked  upon  by  matter,  so  in  a  little  time  such 
a  living  creature  must  be  destroyed,  if  there  is  no  provision 
for  repairing  the  injuries  which  she  must  commit  on  her- 
self, and  those  to  which  she  must  be  exposed  from  without. 
Therefore  a  treasure  of  blood  is  actually  provided  in  the 
heart  and  vascular  system,  full  of  nutritious  and  healing  par- 
ticles, fluid  enough  to  penetrate  into  the  minutest  parts  of 
the  animal ;  impelled  by  the  heart,  and  conveyed  by  the  ar- 
teries, it  pervades  every  part,  builds  up  what  was  broken 
down,  and  sweeps  away  the  old  and  useless  materials.  Hence 
we  see  the  necessity  or  advantage  of  the  heart  and  arterial 
system.  The  heart  consists  of  four  cavities,  from  one  of 
which,  the  blood  is  driven  into  the  arteries  through  the  body, 
by  another,  it  is  received  back  again  by  the  veins  :  it  then 
passes  into  the  third,  whence  it  is  forced  into  the  lungs. 
Having  there  been  revivified  by  coming  in  contact  with  the 
air,  it  is  carried  back  by  a  set  of  veins  into  the  fourth  cavity, 
and  thence  into  that  in  which  it  began  its  course  :  it  is  then 
again  forced  into  the  arteries,  brought  back  by  the  veins, 
and  thus  circulates  till  the  end  of  life.  Each  cavity  of  the 
heart  is  generally  called  into  action  four  thousand  times 
every  hour.  The  arteries,  into  which  the  blood  is  forced, 
branch  in  every  direction  through  the  body,  like  the  roots, 
branches,  and  leaves  of  a  tree,  running  through  the  substance 
fif  the  bones,  and  every  part  of  the  animal,  till  they  are  lost 
in  such  fine  tubes  as  to  be  wholly  invisible.     In  this  man- 


STUUCTURE    OF   THE   HUMAN    BODY.  26l 

tier,  they  distribute  nourishment,  supply  perspiration,  and 
renew  all  the  waste  of  the  system  ;  and  by  passing  through 
glands  in  every  part  of  the  body,  all  the  various  animal  se- 
cretions are  elaborated.  In  the  parts  where  the  arteries  are 
lost  to  the  sight,  the  veins  take  their  rise,  and  in  their  com- 
mencement are  also  imperceptible.  The  blood  is  then  of  a 
dark  colour.  In  this  discoloured  state  it  has  lost  some  of  its 
vital  power ;  but  on  being  driven  through  the  lungs  its  colour 
is  restored.  All  this  provision,  however,  would  not  be  suffi- 
cient, for  the  store  of  blood  would  soon  be  consumed,  and 
the  fabric  would  break  down,  if  there  was  not  a  provision 
for  fresh  supplies.  And  we  actually  fmd  that  on  its  passage 
from  the  lungs  to  the  heart  the  blood  receives  a  supply  of  a 
new  fluid  extracted  from  the  food  by  myriads  of  fine  tubes 
which  carry  it  to  a  larger  one,  that  empties  itself  into  a  large 
vein,  and  being  mixed  with  the  blood  is  conveyed  to  the 
heart.  We  see,  therefore,  by  the  very  imperfect  survey  which 
we  have  been  able  to  take  of  this  subject,  that  the  animal 
man  must  necessarily  be  complex  in  his  corporeal  system, 
and  in  its  operations.  He  must  have  one  great  and  general 
system,  the  vascular,  branching  through  the  whole  circula- 
tion ;  another,  the  nervous,  with  its  appendages  the  organs 
of  sense,  for  every  kind  of  feeling  ;  and  a  third  for  the  ccmi- 
nexion  and  union  of  all  these  parts.  Besides  these  primary 
and  general  systems,  he  requires  others  which  may  be  more 
local  or  confined.  One  for  strength,  support,  and  protec- 
tion ;  another  for  the  requisite  motion  of  the  parts  among 
themselves,  as  well  as  for  moving  from  place  to  place,  the 
muscular  system ;  another  to  prepare  nourishment  for  the 
daily  recruit  of  the  body,  the  digestive  organs;  and  others 
for  the  various  purposes  of  existence. 

Questions. — 1.  What  are  the  uses  of  the  blood  ?  2.  Describe  the 
circulation  of  the  blood.  3.  Describe  the  arteries.  4.  WJiat  changes 
does  the  blood  undergo  in  the  course  of  its  circulation  .■*  5.  How  is 
provision  made  for  a  fresh  supply  of  blood  ?  [Note.  That  cavity  of 
the  heart  from  which  the  blood  is  driven  into  the  arteries  is  called  th« 
left  ventricle  ;  the  next  is  called  the  right  auricle  ;  the  third  the  right 
ventricle  ;  and  the  fourth  the  left  auricle. ~\ 


f^62  THE  HUMAN  VOiCfl. 


LESSON  119.  ''-WK' 

The  Human  Voice. 

£piglot'tis,  a  small  and  thin  piece  of  cartilage,  placed  at  the  back 
of  the  tongue,  and  having  the  office  of  closing  the  glottis,  when 
the  food  is  passing. 

The  parts  employed  in  the  production  of  the  voice  are 
three  in  number,  the  trachea,  or  wind-pipe,  by  which  the 
air  passes  to  and  from  the  lungs ;  the  larynx,  Which  is  a 
short  cylindrical  canal  at  the  head  of  the  trachea  ;  and  the 
glottis,  which  is  a  small  oval  opening  between  two  semicir- 
cular membranes.  The  glottis  being  very  narrow  compared 
with  the  size  of  the  trachea,  the  air  can  never  pass  through 
it  without  acquiring  a  considerable  degree  of  velocity ;  so 
that  the  air  thus  compressed  and  forced  on  communicates,  as 
it  passes,  a  vibratory  motion  to  the  particles  of  the  two  lips 
of  the  glottis,  which  produces  the  sound.  The  sound  thus 
produced  is  reverberated  through  the  different  parts  of  the 
mouth ;  and  it  is  the  mixture  of  different  reverberations, 
well  proportioned  to  one  another,  which  produces  in  the 
human  voice  a  harmony,  whicli  no  instrument  can  equal. 

The  most  wonderful  part  of  the  mechanism  of  the  voice 
is  the  contraction  and  dilatation  of  the  glottis.  It  is  these 
changes  which  produce  all  the  variety  of  tone.  The  diame- 
ter of  the  glottis  never  exceeds  one  tenth  of  an  inch :  now 
suppose  a  person  capable  of  sounding  twelve  notes — to  which 
the  voice  easily  reaches, — there  must  be  the  difference  of 
the  hundred  and  twentieth  part  of  an  inch  for  each  note. 
But  if  we  consider  the  subdivision  of  notes  of  which  the 
voice  is  capable,  the  motion  of  the  sides  of  the  glottis  ap- 
pears still  more  minute.  Suppose  that  a  voice  can  divide  a 
note  into  one  hundred  parts ;  it  will  follow  that  the  different 
openings  of  the  glottis  will  be  twelve  hundred  in  one  tenth 
of  an  inch,  and  it  is  known  that  each  of  these  will  produce 
sounds  perceptibly  different  to  a  good  ear.  But  the  move- 
ment of  each  side  of  the  glottis  being  equal,  it  is  necessary 
to  double  this  number,  and  the  side  of  the  glottis,  therefore, 
actually  divides  the  tenth  of  an  inch  into  twenty-four  hun- 
dred equal  parts. 

Speech  is  articulated  voice,  that  is,  voice  modified  by  the 
action  of  the  palate,  teeth,  tongue,  and  lips.     All  animals 


THE  EAR.  263 

have  a  voice,  but  man  alone  speaks  in  the  sense  now  alluded 
to.  Some  animals,  it  is  true,  have  been  taught  to  pronounce 
a  few  words ;  but  they  express  no  thoughts  by  these  sounds. 
It  is  believed  that  no  sufficient  reason  can  be  drawn  from 
mere  organization,  why  man  invariably  should  possess, 
and  animals  invariably  want  the  power  of  speech.  If  we 
consider  speech  simply  as  a  medium  of  the  reciprocal  ex- 
pressions of  present  feelings  to  the  little  society  of  citizens 
and  friends  of  which  we  are  a  part,  even  in  this  limited  view, 
of  what  inestimable  value  does  it  appear  !  To  communicate 
to  every  one  around  us,  in  a  single  moment,  the  happiness 
which  we  feel  ourselves, — to  express  the  want,  which  we 
have  full  confidence,  will  be  relieved  as  soon  as  it  is  known, 
— or  to  have  the  still  greater  privilege  of  being  ourselves  the 
ministers  of  comfort  to  Mants,  which  otherwise  could  not 
have  been  relieved  by  us,  because  they  could  not  have  been 
discovered, — when  the  heart  which  we  love  is  weighed  down 
with  imaginary  grief,  to  have  it  in  our  power,  by  a  few  sim- 
ple sounds,  to  convert  anguish  itself  into  rapture, — these  are 
surely  no  slight  advantages ;  and  yet  compared  with  the  bene- 
fit which  it  affords  to  man  as  an  intellectual  being,  even  these 
are  inconsiderable.  By  means  of  language,  spoken  or  writ- 
ten, the  opinions  which  are  perishing  in  one  mind,  are  rising 
in  another ;  and  often,  perhaps,  at  ihe  last  fading  ray  of  the 
flame  of  genius,  that  may  have  almost  dazzled  the  world  by 
excess  of  brilliancy,  some  star  may  be  kindling,  which  is  to 
shine  upon  the  intellectual  universe  with  equal  light  and 
glory. 

Questions. — 1.  What  are  the  parts  employed  in  the  production 
of  the  voice?  2.  How  is  the  sound  produced  ?  3.  What  is  the  most 
wonderful  part  of  the  mechanism  of  the  voice  ?  4.  What  is  said  of 
the  divisions  and  subdivisions  of  the  glottis  in  sounding  twelve  notes  .'' 
5.  What  is  speech  ?    6.  Wliat  is  said  of  the  voice  of  animals  ? 


LESSON  120. 

The  Ear. 
Trun'cated,  divided.     Sen'tient,  perceiving. 
The  ear  is  adapted  in  an  eminent  degree  to  the  purpose! 
it  is  designed  to  execute ;  and  it  oiTers  an  inviting  eubject 


284  THE  EAR. 

to  such  as  are  disposed  to  investigate  the  minute  mechanism 
of  an  organ,  which  contributes  remarkably  to  some  of  our 
most  exquisite  and  refined  enjo^^ments.  Though  the  rapid 
glance  of  the  eye,  and  the  immense  distance  to  which  it 
enables  us  to  carry  our  perceptions  have  given  rise  to  some 
of  our  most  pleasurable  and  magnificent  sensations,  still  the 
sense  which  we  are  now  considering  has  contributed  most 
efficiently  to  the  daily  happiness  of  life.  It  enables  us  to 
hold  communication  with  our  fellow  creatures ;  to  improve 
and  exalt  our  understandings  by  the  mutual  interchange  of 
ideas  ;  and  thus  to  increase  the  circle  not  only  of  our  physi- 
cal, but  of  our  moral  relations.  The  charms  of  eloquence 
and  the  pleasure  resulting  from  the  concord  of  sweet  sounds 
are  other  sources  of  intellectual  enjoyment,  which  contribute 
to  place  this  sense  among  the  most  delightful  as  well  as  the 
most  important  we  possess. 

The  organ  of  hearing,  in  its  simplest  form,  consists  of  the 
expansion  of  a  nerve,  gifted  with  its  peculiar  sensitive  quali- 
ties, over  the  surface  of  a  delicate  membrane.  In  man  and 
the  more  perfect  animals,  there  is  an  additional  apparatus 
connected  with  this,  the  design  of  which  is  to  collect  and 
modify  those  pulses  of  the  air  which  are  finally  to  be  im- 
pressed on  the  nervous  membrane.  In  man  this  apparatus 
consists  of  a  piece  of  cartilage,  seated  externally  to  the  head, 
which  contracts  into  a  tube  leading  to  the  internal  parts. 
The  bottom  of  this  tube  is  truncated  obliquely,  and  its  aper- 
ture closed  by  a  firm  membrane  stretched  across  it,  called 
the  drum  of  the  ear,  which  separates  the  external  part  from 
the  succeeding,  or  middle  portion  of  the  organ.  Beyond,  or 
on  the  opposite  side  of  this  membrane,  we  meet  with  a  small 
cavity,  hollowed  out  in  bone.  Of  the  several  openings  into 
it,  there  is  one  more  particularly  demanding  attention.  It 
is  the  internal  aperture  of  a  tube,  the  other  extremity  of 
which  opens  behind  and  above  the  palate.  By  means  of  this 
communication,  the  external  air  is  admitted  into  the  cavity, 
and  equipoises  the  weignt  of  the  atmosphere  on  the  other 
side  of  the  membrane.  Across  the  cavity  there  is  extended, 
though  by  no  means  in  a  straight  line,  a  series  of  Jittle  bones, 
the  exterior  one  of  which  is  attached  to  the  membrane  we 
have  just  mentioned,  the  most  internal  set  being  firmly  con-* 
nected  with  another  membrane,  which,  in  conjunction  with 
it,  shuts  up  the  entrance  to  s^  still  more  deepened  cavity, 


MUSIC.  265 

called  the  labyrinth  of  the  ear.  This  last  hollow,  excavated 
as  it  were  in  the  solid  bone,  consists  of  a  middle  portion  of 
irregular  figure,  and  of  different  channels,  which  proceed 
from  it  in  various  directions,  and,  finally,  return,  with  one 
exception  to  the  same  chamber.  All  these  passages  are 
lined  by  a  membrane,  on  which  the  sentient  extremity  of 
the  auditory  nerve  is  expanded  in  different  shapes  ;  from 
these  it  is  collected  into  one  trunk  and  goes  on  to  join  a 
particular  part  of  the  brain,  and  thus  completes  the  com- 
munication between  the  external  agent  and  the  sensorial 
organ. 

Questions. — 1.  What  is  the  organ  of  hearing  in  its  simplest 
form  ?  2.  What  apparatus  is  connected  with  this  in  man  ?  3.  De- 
scribe the  tube  and  cavity  beyond  it.  4.  What  opening  deserves  par- 
ticular attention  ?  5.  What  is  the  use  of  it  ?  6.  What  extends  across 
the  cavity  ?  7.  Of  what  does  the  labyrinth  consist  ?  8.  On  what  ig 
the  auditory  nerve  expanded  ?  and  what  does  it  join  when  collected 
into  one  trunk .'' 


LESSON  121. 

Music. 

Music  is  the  art  of  combining  tunable  sounds  in  a  man- 
ner agreeable  to  the  ear.  It  is  an  expression  of  feeling, 
which,  almost  like  verbal  discourse,  may  be  said  to  be  a  lan- 
guage, since  it  is  the  utterance  of  thought  and  emotion  from 
heart  to  heart.  But  music  has  a  voice,  as  independent  of 
the  mere  arbitrary  forms  of  speech,  as  the  tears  of  gratitude, 
or  the  smiles  of  love,  that  may  indeed,  give  eloquence  to 
words,  but  require  no  tcords  to  render  them  eloquent. 
Though,  when  very  strictly  considered,  even  the  pure  and 
almost  spiritual  delight  of  music,  may  perhaps  be  counted 
only  a  pleasure  of  sense,  yet  it  approaches,  by  so  many 
striking  analogies,  to  the  nature  of  our  intellectual  enjoy- 
ments, that  it  may  almost  be  said  to  belong  to  that  class.  In 
its  relation  to  the  general  pleasures  of  common  minds,  it  is 
not  to  be  considered  as  a  mere  pastime  or  relaxation  ;  it  as- 
sumes a  far  higher  character,  and  it  may  be  said,  at  least,  to 
be  the  infellectual  luxury  of  those,  who  are  incapable  of  any 
other  luxury  that  deserves  so  honourable  a  name.  And  it  is 
well,  that  there  should  be  some  such  intermediate  pleasure 
23 


MUSIC, 

of  this  sort,  to  withdraw  for  a  while  the  dull  and  the  sensual, 
from  the  grosser  existence  in  which  they  may  be  sunk,  and 
to  give  them  some  glimpses,  at  least,  of  a  state  of  purer  en- 
joyment, than  that  which  is  to  be  derived  from  the  sordid 
gains,  and  sordid  luxuries  of  common  life.  Of  the  influence, 
which  music  has  upon  the  general  character,  when  cultivated 
to  great  refinement,  there  are  different  opinions.  But  of  its 
temporary  influence,  as  a  source  of  tranquillii^ing  delight, 
there  can  be  no  doubt. 

Who  ne'er  has  felt  her  hand  assuasive  steal 

Along  his  heart — that  heart  will  never  feel. 

'Tis  hers  to  chain  the  passions,  sooth  the  soul. 

To  snatch  the  dagger,  and  to  dash  the  bowl 

From  Murder's  hand ;  to  smooth  the  couch  of  Care, 

Extract  the  thorns,  and  scatter  roses  there. 

To  her,  Religion  owes  her  holiest  flame : 

Her  eye  looks  heaven-ward,  for  from  heaven  she  came. 

And  when  Religion's  mild  and  genial  ray. 

Around  the  frozen  heart  begins  to  play, 

Music's  soft  breath  falls  on  the  quivering  light ; 

The  fire  is  kindled,  and  the  flame  is  bright ; 

And  that  cold  mass,  by  either  power  assail'd, 

Is  warm'd — made  liquid — and  to  heaven  exhal'd, 

PlERPONT. 

The  phenomena  of  music,  in  addition  to  their  general  in-» 
terest,  are  truly  worthy  of  our  astonishment,  from  that 
striking  diversity  of  organic  power  in  the  perception  of 
melody  and  still  more  of  harmony  which  they  exhibit  in  dif^ 
ferent  individuals,  in  whom  all  other  circumstances  are  ap- 
parently the  same.  This  diversity  has  often  attracted  the 
attention  of  philosophers,  and  has  led  even  those  who  have 
no  great  tendency  to  speculation  of  any  kind,  to  wonder  at 
least,  which  is  the  first  step  of  all  philosophizing.  In  the 
present  instance,  however  unfortunately,  this  first  step  is  the 
only  step  which  philosophers  have  been  able  to  take.  If 
the  want  of  a  musical  ear  had  involved  either  a  general  de- 
fect of  hearing,  or  a  general  slowness  of  discrimination  in 
other  cases  of  nice  diversity,  the  wonder  would  not  have 
been  great.  But  those  who  are  without  ear  for  music  per- 
^ive  as  readily  as  others  the  faintest  whisper ; — they  dis- 
tinguish like  them,  the  faintest  shades  of  difference  in  the 


I^AINTING. 


26'}' 


ttiere  articulations  of  sound  which  constitute  the  varieties  of 
language,  nor  the  articulations  only,  but  the  differences  also 
of  the  mere  tones  of  affection  or  displeasure,  grief  or  gayety, 
which  are  so  strikingly  analogous  to  the  varied  expression 
of  musical  feeling ;— and  their  power  of  discrimination  in 
every  other  case  in  which  the  judgment  can  be  exercised, 
is  not  less  perfect. 

That  the  ear  may  be  improved  by  cultivation,  or  in  other 
words,  by  nice  attention  to  the  differences  of  musical  sound, 
every  one  knows ;  and  if  this  attention  can  enable  us,  even 
in  mature  life,  to  distinguish  sounds  as  different  in  them- 
selves, which,  but  for  the  habitual  attention,  we  should  have 
regarded  as  the  same,  it  may  well  be  supposed  that  continued 
inattention,  from  earliest  infancy,  may  render  us  insensible 
of  musical  relations  still  more  obvious  and  precise,  than 
those  which  we  have  thus  only  learned  to  distinguish  ; — or, 
which  is  the  same  thing,  that  continued  attention  from  in- 
fancy to  slight  musical  differences  of  sound  may  render  us 
capable  of  distinguishing  tones  as  very  dissimilar,  the  dif- 
ferences of  which,  however  obvious  at  present,  we  should 
scarcely,  but  for  such  original  attentive  discrimination,  have 
been  able  to  detect. 

Questions. — 1.  What  is  music  ?  2.  What  renders  the  plienomena 
of  music  worthy  of  astonishment  ?  3.  What  may  be  supposed  to  result 
from  inattention  to  the  differences  of  musical  sounds  ?   4.  Attention  ? 


LESSON  122. 

Painting. 

Pen'cil,  an  instrument  used  by  painters  for  laying  on  colours ;  the 
finer  sorts  are  made  of  camels'  hair,  or  sometimes  of  the  down 
of  swans. 

The  art  of  distributing  lights  and  shades  is  called  clair  obscure, 
or  chiaro-scuro. 

The  art  of  painting  gives  the  most  direct  and  expressive 
representation  of  objects  ;  and  it  was,  doubtless,  for  this 
reason  employed  by  many  nations,  before  the  art  of  writing 
was  invented,  to  communicate  their  thoughts,  and  to  convey 
intelligence  to  distant  places.  The  pencil  may  be  said  to 
write  a  universal  language ;  for  every  one  can  instantly  un- 
derstand the  meaning  of  a  painter,  provided  he  be  faithful  to 


268  PAINTING. 

the  rules  of  his  art.     His  skill  enables  him  to  display  the  j 

various  scenes  of  nature  at  one  view  ;  and  by  his  delineation  J 

of  the  striking  effects  of  passion,  he  instantaneously  affects  \ 

the  soul  of  the  spectator.     Silent  and  uniform  as  is  the  ad-  J 

dress  which  a  good  picture  makes  to  us,  yet  it  penetrates  so  ] 

deeply  into  our  aflections,  as  to  appear  to  exceed  the  powers  > 
of  eloquence. 

Painting  is  the  most  imitative  of  all  the  arts.     It  gives  to  j 

us  the  very  forms  of  those,  whose  works  of  genius,  or  of  vir-  J 

tue,  have  commanded  or  won  our  admiration,  and  transmits  ^ 

them  from  age  to  age,  as  if  not  life  merely,  but  immortality  j 

flowed  in  the  colours  of  the  artist's  pencil ;  or,  to  speak  of  j 

its  still  happier  use,  it  preserves  to  us  the  lineaments  of  those  ,1 

whom  we  love,  when  separated  from  us  either  by  distance  I 

or  the  t©mb.     How  many  of  the  feelings,  which  we  should  I 

most  regret  to  lose,  would  be  lost  but  for  this  delightful  art,  ] 

— feelings  that  ennoble,  by  giving  us  the  wish  to  imitate  I 
what  was  noble  in  the  moral  hero  or  sage,  on  whom  we  gaze, 

or  that  comfort  us,  by  the  imaginary  presence  of  those  whose  j 

affection  is  the  only  thing  dearer  to  us,  than  even  our  admi-  ] 

ration  of  hcr'oism  and  wisdom.     The  value  of  painting  will,  ^ 

indeed,  best  be  felt  by  those  who  have  lost,  by  death,  a  pa-  \ 

rent  or  much-loved  friend,  and  who  feel  that  they  should  not  j 

have  lost  every  thing,  if  some  pictured  memorial  had  still  l 

remained,  I 

Paintings,  in  regard  to  their  subjects,  are  called  historical,  ' 

landscape,  or  portrait ;  and  in  regard  to  the  painters,  they  I 

are  divided  into  schools  or  countries ;  as  the  Italian,  Ger-  1j 

man,    French,  English,   and   other   schools.     Each  of  the  ^ 

schools  has  treated  the  practice  of  painting  in  its  peculiar  ^ 

manner,  and  each  with  exquisite  beauty  and  admirable  ef-  1 

feet.     The  great  component  parts  of  painting  are,  invention,  , 

or  the  power  of  conceiving  the  materials  proper  to  be  intro-  i 

duced  into  a  picture  ;  composition,  or  the  power  of  arranging  l 

them  ;  design,  or  the  power  of  delineating  them  ;  the  manage-  ] 

ment  of  lights  and  shades ;  and  the  colouring.     Invention  j 

consists  principally  in  three  things,  the  choice  of  a  subject  ' 

properly  within  the  scope  of  the  art ;  the  seizure  of  the  most  1 

striking  and  energetic  moment  of  time  for  representation ;  : 

and  the  discovery  and  selection  of  such  objects,  and  such  ; 

probable  incidental  circumstances,  as,  combined  together,  ^ 

may  best  tend  to  develope  the  story,  or  augment  the  interest  i 


PAINTING.  269 

of  the  piece.  In  this  part  of  the  art,  there  is  a  cartoon  of 
Raphael,  which  furnishes  an  example  of  genius  and  sagacity. 
It  represents  the  inhabitants  of  Lystra  about  to  offer  sacri- 
fice to  Paul  and  Barnabas.  It  was  necessary  to  let  us  into 
the  cause  of  all  the  motion  and  hurry  before  us ;  according- 
ly, the  cripple,  whom  they  had  miraculously  healed,  appears 
in  the  crowd  :  observe  the  means  which  the  painter  has  used 
to  dintinguish  this  object,  and  of  course  to  open  the  subject 
of  his  piece.  His  crutches,  now  useless,  are  thrown  to  the 
ground  ;  his  attitude  is  that  of  one  accustomed  to  such  sup- 
port, and  still  doubtful  of  his  limbs ;  the  eagerness,  the  im- 
petuosity, with  which  he  solicits  his  benefactors  to  accept 
the  honours  destined  for  them,  point  out  his  gratitude  and 
the  occasion  of  it.  During  the  time  that  he  is  thus  busied, 
an  elderly  citizen  of  some  consequence,  by  his  appearance, 
draws  near,  and  lifting  up  the  corner  of  his  vest,  surveys 
with  astonishment  the  limb  newly  restored  ;  whilst  a  man 
of  middle  age  and  a  youth,  looking  over  the  shoulder  of  the 
cripple,  are  intent  on  the  same  object.  The  wit  of  man 
could  not  devise  means  more  certain  of  the  end  proposed ; 
such  a  chain  of  circumstances  is  equal  to  a  narration. 

In  the  cartoon  of  Paul  preaching  at  Athens,  the  elevated 
situation,  and  energetic  action  of  the  apostle,  instantly  de- 
note him  the  hero  of  the  piece,  whilst  the  attentive  but 
astonished  circle  gathered  around  him,  receive,  as  it  were, 
light  from  him,  their  centre,  and  unequivocally  declare  him 
the  resistless  organ  of  divine  truth. 

Questions. — 1.  What  are  paintings  in  regard  to  their  subjects  .-* 
2.  To  the  painters  ?  3.  What  are  the  great  component  parts  of  paint- 
ing .''  4.  In  what  three  things  does  invention  consist  ?  5.  What  car- 
toon of  Raphael  is  an  example  in  this  part  of  the  art?  [Note.  En- 
gravings, taken  originally  from  the  cartoons  of  Raphael,  are  sometimes 
inserted  in  Bibles.  That  of  Peter  and  John  healing  the  cripple  at 
the  beautiful  gate  of  the  temple,  and  that  of  Paul  preaching  at  Athens, 
are  common.] 

23* 


270  SCULPTUftfe. 


LESSON  123. 

Sculpture. 
Consifit'ence,  degree  of  density  or  rarity. 
To  ascertain  when  the  art  of  sculpture  was  first  practised, 
and  by  wliat  nation,  is  beyond  human  research.     We  may 
safely  conjecture,  however,  that  it  was  ahnost  one  of  the 
original  propensities  of  man.     This  will  still  appear  in   the 
ardent  and   irresistible  impulse  of  youth  to  make  represen- 
tations of  objects  in  wood,  and  the  attempts  of  savages  to  em- 
body their  conceptions  of  their  idols.     A  command  from  the 
author  of  our  being  was  necessary  to  prevent  the  ancient  Is- 
raelites from  making  graven  images  ;  and  the  inhabitants  of 
the  rest  of  the  earth  possessed  similar  propensities.     The  de- 
scriptions in  the  Scriptures  demonstrate  that  the  art  had  been 
brought  to  great  perfection  at  the  period  of  which  they  treat. 
It  is  necessary  to  make  a  distinction  between  carving  and 
sculpture  :  the  former  belongs  exclusively  to  wood,  and  the 
latter  to  stone  or  marble.     It  is  probable  that  every  essay  at 
imitating  animated  objects  was  in  each  nation  made  original- 
ly in  wood,     But  they  soon  discovered,  doubtless,  that  wood 
was  incapable    of  a   durability    commensurate  with  their 
wishes  ;  they  adopted,  therefore,  a  close  grained  and  beau- 
tiful granite,  which  not  only  required  tools  of  iron,  but  those 
of  the  most  perfectly  tempered  steel,  to  cut  it ;  and  with 
such  they  have  left  us  at  this  very  distant  time  vast  num- 
bers of  excavated  figures,  as  complete  and  as  little  injured 
as  if  executed  within  our  own  memory.     The  acknowledged 
masters  of  the  sublime  art  of  sculpture  are  the  ancient  Greeks^ 
to  whom  every  nation  of  the  earth  still  pays  a  willing  homage, 
and  from  whose  matchless  works  each  sculptor  is  happy  to 
concentrate  and  improve    his   observations  on  the   human 
figure,  presented  by  them  to  his  contemplation  in  its  most 
graceful  perfection.     Such  have  been  the  excellence  and 
correctness  of  their  imitations  of  nature,  and  the  refined 
elegance  of  their  taste,  that  many  of  their  works  are  men- 
tioned, as  efforts  never  to  be  exceeded  or  perhaps  equalled. 
Statuary  is  a  branch  of  sculpture  employed  in  the  making 
of  statues.     The  term  is  also  used  for  the  artificer  himseK 
Phidias  was  the  greatest  statuary  among  the  ancients,  and 


THE  LOVE   OF  NATURE.  271 

Michael  Angelo  among  the  moderns.  Statues  are  not  only 
formed  with  the  chisel  from  marble,  and  carved  in  wood,  but 
they  are  cast  in  plaster  of  Paris,  or  other  matter  of  the  same 
nature,  and  in  several  metals,  as  lead,  brass,  silver,  and  gold. 
The  process  of  casting  in  plaster  of  Paris  is  as  follows  :  the 
plaster  is  mixed  with  water,  and  stirred  until  it  attains  a  pro- 
per consistence  ;  it  is  then  poured  on  any  figure,  for  instance, 
a  human  hand,  or  foot,  previously  oiled  in  the  slightest  man- 
ner possible,  which  will  prevent  the  adhesion  of  the  plaster  : 
after  a  few  minutes  the  plaster  will  dry  to  the  hardness  of 
soft  stone,  taking  the  exact  impression  of  every  part,  even 
the  minutest  pores  of  the  skin.  This  impression  is  called 
the  mould.  When  taken  from  the  figure  that  produced  it, 
and  slightly  oiled,  plaster,  mixed  with  water  as  before,  may 
be  poured  into*it,  and  it  must  remain  until  it  is  hardened  ; 
if  it  be  then  taken  from  the  mould,  it  will  be  an  exact  image  of 
the  original  figure.  When  the  figure  is  flat,  having  no  deep 
hollows  or  high  projections,  it  may  be  moulded  in  one  piece, 
but  when  its  surface  is  much  varied,  it  must  be  moulded  in 
many  pieces  fitted  together,  and  held  in  one  or  more  outside 
or  containing  pieces.  This  useful  art  supplies  the  painter 
and  sculptor  with  exact  representations  from  nature,  and 
multiplies  models  of  all  kinds.  It  is  practised  in  such  per- 
fection, that  casts  of  the  antique  statues  are  made  so  pre- 
cisely like  the  originals  in  proportion,  outline,  and  surface, 
that  no  difference  whatever  is  discoverable,  excepting  in  co- 
lour and  materials; 

Questions.— 1.  What  is  said  of  the  origin  of  sculpture  ?  2.  How 
does  sculpture  differ  from  carving  ?  3.  What  is  said  of  this  art  as  it 
existed  among  the  ancient  Greeks  ?  4.  Define  the  word  statuary  in 
both  senses.  5.  How  are  statues  formed  .'*  6.  What  is  the  process 
of  casting  in  plaster  of  Paris  ?  7.  Of  what  use  is  the  art  of  casting 
to  the  painter  and  sculptor  ? 


LESSON  124. 

77ie  Love  of  Nature. 

Whkn  the  mind  becomes  animated  with  a  love  of  natui^e^ 
nothing  is  seen  tha  does  not  become  an  object  for  curiosity 


S72  THE  IMPORTANCE  OF  NATURAL  PHILOSOPHY. 

and  inquiry.  A  person  under  the  influence  of  this  principle 
can  converse  with  a  picture,  and  find  an  agreeable  com- 
panion in  a  statue.  He  meets  with  a  secret  refreshment  in 
a  description  ;  and  often  feels  a  greater  satisfaction  in  the 
prospect  of  fields  and  meadows,  than  another  does  in  the 
possession.  It  gives  him  indeed  a  kind  of  property  in  every 
thing  he  sees  ;  and  makes  the  most  rude  uncultivated  parts 
of  nature  administer  to  his  pleasures ;  so  that  he  looks  upon 
the  world,  as  it  were,  in  another  light,  and  discovers  in  it  a 
multitude  of  charms,  that  conceal  themselves  from  the  gene- 
rality of  mankind.  A  river  is  traced  to  its  fountain ;  a 
flower  to  its  seed  ;  and  an  oak  to  its  acorn.  If  a  marine 
fossil  lies  on  the  side  of  a  mountain,  the  mind  is  employed 
in  the  endeavour  to  ascertain  the  cause  of  its  position.  If  a 
tree  is  buried  in  the  depths  of  a  morass,  the  history  of  the 
world  is  traced  to  the  deluge  ;  and  he  who  grafts,  inoculates, 
and  prunes,  as  well  as  he  who  plants  and  transplants,  will 
derive  an  innocent  pleasure  in  noting  the  habits  of  trees  and 
their  modes  of  culture  ;  the  soils  in  which  they  delight ;  the 
shapes  into  which  they  mould  themselves ;  and  will  enjoy  as 
great  a  satisfaction  from  the  symmetry  of  an  oak,  as  from  the 
symmetry  of  an  animal.  Every  tree  that  bends,  and  every 
flower  that  blushes,  even  a  leafless  copse,  a  barren  plain, 
the  cloudy  firmament,  and  the  rocky  mountain,  are  objects 
for  his  attentive  meditation.     For, 

To  him  who  in  the  love  of  Nature  holds 

Communion  with  her  visible  forms,  she  speaks 

A  various  language ;  for  his  gayer  hours 

She  has  a  voice  of  gladness,  and  a  smile 

And  eloquence  of  beauty,  and  she  glides 

Into  his  darker  musings,  with  a  mild 

And  gentle  sympathy,  that  steals  away 

Their  sharpness,  ere  he  is  aware.  Bryant. 


LESSON  125. 

The  Importance  of  Natural  Philosophy. 

With  thee,  serene  Philosophy,  with  thee. 
And  thy  bright  garland,  let  me  crown  my  song : 


THE  IMPORTANCE  OF  NATURAL  PHILOSOPHY.  5^7^ 

Effusive  source  of  evidence  and  truth  ! 
Without  thee,  what  were  unenlightened  man? 
A  savage  roaming  through  the  woods  and  wilds, 
In  quest  of  prey  ;  and  with  the  unfashioned  fur 
Rough  clad  :  devoid  of  every  finer  art, 
And  elegance  of  life.     Nor  happiness 
Domestic,  mixed  of  tenderness  and  care, 
Nor  moral  excellence,  nor  social  bliss, 
Nor  guardian  law  were  his ;  nor  various  skill 
To  turn  the  furrow ;  nor  to  guide  the  tool 
Mechanic  ;  nor  the  heaven-conducted  prow 
Of  navigation  bold,  that  fearless  braves 
The  burning  line,  or  dares  the  wint'ry  pole. 

Thomson. 

What  can  be  more  gratifying  than  to  become  acquainted 
with  the  wonderful  laws  of  matter  and  motion  ;  with  the 
grand  mechanical  powers  ;  and  the  ingenious  and  admirable 
application  of  them  to  numberless  purposes  of  human  in- 
dustry, convenience,  and  comfort?  What  more  pleasing 
than  to  know  the  nature  and  properties  of  the  element  in 
which  we  live  ;  to  understand  the  laws  on  which  the  motion 
and  pressure  of  fluids  depend ;  to  be  able  to  ascertain  the 
specific  gravities,  or  the  relative  weight  of  diflferent  bodies ; 
and  to  be  made  acquainted  with  those  newly-discovered 
principles,  by  means  of  which  the  aspiring  genius  of  man 
has  dared  to  soar  through  the  trackless  regions  of  the  air, 
and  to  explore,  unhurt,  the  capacious  bosom  of  the  deep  ? 
What  can  be  more  interesting  or  more  delightful,  than  to 
accompany  the  rays  of  light  in  their  rapid  journey  from  the 
sun ;  to  observe  the  various  effects  of  reflection  and  refrac- 
tion ;  to  analyze  distinctly  the  principle  of  light ;  to  grasp 
the  fading  colours  of  the  rainbow ;  to  understand  the  laws 
of  vision ;  and  to  view  the  wonderful  and  happy  application, 
which  has  been  made  of  the  grand  principles  of  optics,  to 
the  promotion  of  physical  and  astronomical  science  ?  What 
more  astonishing  than-  the  exquisite  nature  of  that  most  sub- 
tile, all-pervading  fluid,  which,  when  collected,  produces 
such  powerful  effects  upon  the  human  frame,  which  sports 
in  the  northern  lights,  and  flashes  amidst  the  storm ;  and 
which,  by  the  penetrating  genius  and  art  of  man,  ha-;  even 
been  rendered  tractable  and  obedient  to  his  will  ?    To  be 


^H 


MYTHOLOGY. 


made  acquainted  with  the  surprising  laws  of  magnetic  bodies, 
with  the  polarity  of  the  needle,  and  the  amazing  changes 
which  a  knowledge  of  this  most  remarkable  property  has  ef- 
fected in  the  widely-extended  intercourse  of  different  na- 
tions by  means  of  improved  navigation,  are  certainly  objects 
of  the  greatest  utility,  and  interesting  and  instructive  in  the 
highest  degree.  While  you  contemplate  the  admirable  laws 
of  the  planetary  system,  you  will,  doubtless,  be  struck  with 
reverence  and  awe  at  the  great  First  Cause,  which  originally 
established,  and  which  continually  maintains  them  in  order 
and  in  being. 

Curious  to  search  what  binds  old  Ocean's  tides, 
What  through  the  various  year  the  seasons  guides, 
What  shadows  darken  the  pale  queen  of  night. 
Whence  she  renews  her  orb  and  spreads  her  light. 

You  will  take  a  pleasing  survey  of  those  grand  movements 
in  the  heavenly  bodies,  to  which  the  sweet  interchange  of 
day  and  night,  the  grateful  succession  of  the  seasons,  the 
occurrence  of  eclipses,  and  the  regular  flowing  and  ebbing 
of  the  tides,  may  be  justly  ascribed.  With  the  mind's  eye 
you  will  even  cast  a  glance  into  that  universe  of  worlds, 
which,  orbit  within  orbit,  system  combined  with  system,  the 
daring  genius  of  philosophy  has  ventured  to  descry  in  the 
regions  of  infinite  space ;  and  while  absorbed  in  these  sub- 
lime speculations,  you  will  be  ready  to  exclaim  with  the  in- 
spired poet  of  Israel,  "  The  heavens  declare  the  glory  of 
God,  and  the  firmament  proclaimeth  his  handy  work  :"  or  fo 
break  forth  in  the  beautiful  strains  of  Thomson — 

"  These,  as  they  change,  Almighty  Father,  these 

Are  but  the  varied  God  ;  the  rolling  year  is  full  of  Thee  !" 


LESSON  126. 

Mythology. 

Mythology  comprehends  all  those  fabulous  details  con- 
cerning the  objects  of  worship,  which  were  invented  and 
propagated  by  men  who  lived  in  the  early  ages  of  the 
world,   and  transmitted   to  succeeding  generations,  either 


ACCOUNT  OP  THE  PRINCIPAL  HEATHEN  GODS.  275 

by  oral  traditions,  or  written  records.  Fable  is  a  creature 
of  the  human  imagination,  and  owes  its  birth  to  that  love  of 
the  marvellous,  by  which  man  is  so  peculiarly  distinguished. 
Many  circumstances  conspired  to  extend  and  establish  the 
empire  of  fable.  The  legislature  employed  fiction  as  the 
most  effectual  means  of  civilizing  a  rude  world ;  philoso- 
phers, poets,  and  musicians,  made  this  a  vehicle  of  instruc- 
tion to  the  savage  tribes.  A  fondness  for  fable,  and  her  atr 
tendants  allegory  and  personification,  early  characterized 
the  Orientals.  The  boldness  and  the  extravagance  of  their 
mythology  are  to  be  attributed,  in  a  great  measure,  to  the 
genial  warmth  of  the  climate,  and  to  the  fertility  of  the  soil ; 
to  the  face  of  nature  perpetually  blooming  around  them ; 
and  to  the  opportunity  they  had  of  contemplating  the  heaven 
ly  bodies,  continually  shining  under  a  cloudless  sky.  These 
were  soon  considered  as  the  residence  of  Divine  intelligence, 
and  worshipped,  together  with  the  elements,  as  deities.  The 
historians  of  antiquity  were  all  poets.  To  immortalize  the 
heroes,  whose  deeds  they  described,  they  elevated  them  to 
the  skies,  and  bestowed  on  them  the  names  of  the  celestial 
luminaries.  The  sculptor  and  the  painter  exercised  all  their 
skill  to  encourage  this  strange  delusion.  The  use  of  hiero- 
glyphics was  another  fertile  source  of  error.  The  minutest 
animals  and  plants  were  worshipped  as  emblems  of  Deity. 

Questions. — 1.  What  does  mythology  comprehend?  2.  What  is 
Fable  ?  3.  By  whom,  and  for  what  ends,  was  fiction  employed .?  4. 
What  characterized  the  Orientals,  or  eastern  nations  ?  5.  What  oc- 
casioned their  peculiar  mythology  ?  6.  Why  did  ancient  historians 
encourage  mythology  J  7.  To  what  other  causes  is  this  delusion  to 
bo  attributed? 


LESSON  127. 

Account  of  the  principal  Heathen  Gods. 

Before  the  birth  of  our  Saviour,  the  Jews  were  the  only 
nation  of  the  v/orld  who  worshipped  the  true  God.  All  the 
other  nations  worshipped  different  imaginary  beings,  which 
exisfeed  only  in  their  absurd  and  ridiculous  fancies.  Most 
of  these  false  gods,  however,  have  now  become  forgotten, 
together  with  the  nations  that  believed  in  them ;  but  it  is 


276  ACCOUNT  OF  THE  PRINCIPAL  HEATHEN  GODS. 

necessary  to  preserve  a  knowledge  of  the  gods  and  goddesses 
worshipped  by  the  Greeks  and  Romans,  as  they  are  much 
spoken  of  in  the  finest  writings  of  antiquity,  and  are  still 
frequently  mentioned  both  in  poetry  and  in  prose.  The 
most  ancient  of  their  gods  were  Cha'os,  and  his  son  Er'e- 
bus ;  or  confusion,  and  darkness.  Saturn,  one  of  their  de- 
scendants, is  the  same  as  Time  :  his  reign  is  called  the 
Golden  Age ;  and  it  is  said,  that  the  earth  then  produced 
corn  and  fruits  without  labour,  and  justice  prevailed  among 
all  mankind.  Saturn  was  deposed  by  his  son  Jupiter,  called 
also  Jove;  who  then  divided  his  father's  power  between 
himself  and  his  two  brothers,  Neptune  and  Pluto.  Jupiter 
was  to  reign  over  heaven  ;  and  he  was  said  to  hold  his  court, 
or  council  of  the  gods,  on  the  top  of  Olym'pus,  a  mountain 
in  Thes'saly.  He  is  called  by  tlie  ancient  poets,  the  king 
of  gods  and  men  ;  and  the  eagle  is  represented  as  being  the 
bearer  of  his  thunderbolts.  Neptune,  the  god  of  the  sea,  is 
represented  with  a  trident,  or  fork  with  three  teeth  in  his 
hand  instead  of  a  sceptre.  He  was  drawn  in  his  chariot  by 
sea-horses,  with  his  son  Triton  blowing  a  trumpet  made  of  a 
shell,  and  dolphins  playing  round  him. 

The  dominions  of  Pluto,  the  god  of  the  infernal  regions, 
were  divided  into  two  parts,  called  Tar'tarus  and  Elys'ium. 
Tartarus  was  the  place  where  the  souls  of  the  wicked  were 
punished,  and  Elysium  was  the  scene  of  perpetual  happiness 
allotted  to  the  good.  The  passage  from  the  earth  to  these 
regions  was  across  the  river  A'cheron,  over  which  the  de- 
parted spirits  were  conveyed  by  an  old  boatman,  named 
Cha'ron  ;  and  the  further  bank  was  also  guarded  by  a  dog 
with  three  heads,  named  Cer'berus.  There  were  two  re- 
markable rivers  of  Tartarus :  one  named  Styx,  which  the 
gods  used  to  swear  by  when  they  intended  to  make  their 
oath  very  solemn  ;  and  another  named  Le'the,  which  caused 
whoever  bathed  in  it  to  forget  every  thing  that  was  past. 
Mars,  the  son  of  Jupiter,  was  the  god  of  war.  ApoPlo,  like- 
wise the  son  of  Jupiter,  was  the  god  of  music,  poetry,  and 
medicine.  He  is  also  represented  as  driving  the  chariot  of 
the  sun,  drawn  by  four  horses  abreast ;  or  rather,  he  is  the 
sun  itself.  As  a  mark  of  affection,  he  intrusted  this  chariot 
one  day  to  his  son  Phaeton  ;  who  was  killed  by  being  thrown 
out  of  it,  but  not  till  after  he  had  set  a  part  of  the  earth  on 
fir©.     Apollo  is  called  also  Phcebus,  and  Hype'rion ;  and  is 


ACCOUNT  OP  THE  PRINCIPAL  HEATHEN  GODS.  97T 

represented  as  a  beautiful  young  man,  without  a  beard,  and 
with  graceful  hair.  Mercury,  a  son  of  Jupiter,  was  the 
messenger  of  the  gods ;  and  is  therefore  represented  with 
wings  to  his  cap  and  his  feet.  He  was  said  to  be  the  in- 
ventor of  letters,  and  hence  he  is  the  god  of  eloquence ;  and 
was  the  god  of  trade,  and  thence  also  of  thieves.  He  was 
called  also  Her'mes ;  and  is  represented  as  carrying  a  wand, 
called  cadu'ceus,  with  two  serpents  twisting  round  it.  Vul- 
can, the  god  of  fire  and  of  smiths,  was  the  artificer  of  heaven  ; 
and  made  the  thunderbolts  of  Jupiter,  and  the  armour  and 
palaces  of  the  gods.  It  is  said  that  one  of  his  principal 
forges  was  within  Mount  Etna.  He  is  "called  also  Mul'ci- 
ber. 

The  foregoing  are  the  principal  gods,  but  there  were 
many  of  a  second  or  still  lower  order.  Bac'chus  was  the 
god  of  wine,  and  was  crowned  with  leaves  of  the  vine  and 
the  ivy.  E'olus  was  the  god  of  the  winds  :  the  north  wind 
was  called  Bo'reas,  the  south  wind  Au'ster,  the  east  wind 
Eu'rus,  and  the  west  wind  Zeph'yrus.  Mo'mus  was  the 
god  of  satire,  and  likewise  of  laughter  and  jokes.  Plu'tus 
was  the  god  of  riches.  Hy'men  was  the  god  of  marriage  : 
he  is  represented  with  the  burning  torch.  Cu'pid  was  th« 
god  of  love  :  he  is  represented  as  a  beautiful  child,  but  blind 
or  hoodwinked,  and  carries  a  bow  and  arrows.  Ja'nus,  a 
god  with  two  faces,  looking  forward  and  backward,  had  a 
temple  which  v/as  open  in  time  of  war,  and  shut  in  peace. 
EsGula'pius  was  an  inferior  god  of  medicine,  below  Apollo: 
he  is  represented  as  accompanied  by  a  serpent,  which  was 
thought  the  most  long-lived  of  all  animals.  Pan  was  the 
god  of  shepherds ;  and  he  is  represented  as  having  horns, 
and  as  carrying  the  musical  instrument,  now  called  Pan's 
pipes.  There  were  other  rural  deities  called  Sat'yrs,  Fauns, 
and  Syl'vans  :  their  figures  were  half  man  and  half  goat, 
and  they  dwelt  chiefly  in  forests.  Every  river  also  was  sup* 
posed  to  have  its  own  god  ;  who  was  drawn  with  a  long 
beard,  a  crown  of  reeds,  and  leaning  on  an  urn.  There  were 
likewise  a  great  number  of  demi-gods,  or  half-gods;  the 
principal  one  of  these  was  Her'cules ;  who  was  accounted 
the  god  of  strength,  from  his  living  performed  some  wonder- 
ful undertakings,  ctOled  his  Twelve  Labours.  He  is  repre- 
•«nted  leaning  on  a  iarge  club,  and  wearing  a  lion's  skin. 

24  -.1 


S78   ACCOUNT  OF  THE  PRINCIPAL  HEATHEN  GODDESSES, 


LESSON  128. 

Account  of  the  principal  Heathen  Goddesses. 

Ju'no  was  the  wife  of  Ju'piter,  and  was  of  course  the 
queen  of  heaven.  She  is  represented  as  drawn  by  peacocks 
in  a  chariot  of  gold.  Her  favourite  messenger  was  I'ris  the 
goddess  of  the  rainbow.  Miner'va,  a  daughter  of  Jupiter, 
was  the  goddess  of  wisdom  and  of  war.  She  was  repre- 
sented in  complete  armour,  bearing  a  shield,  called  segis, 
with  a  head  on  it,  so  terrible,  that  every  one  who  looked  on 
it  was  turned  into  stone.  She  was  likewise  the  patroness 
of  spinning,  needle-work,  and  embroidery.  She  was  called 
also  Pal'las,  and  her  principal  emblem  was  the  owl.  Dian'a 
was  the  twin  sister  of  Apollo ;  and  as  he  drove  the  chariot 
of  the  sun,  so  she  presided  in  that  of  the  moon.  She  was 
the  goddess  of  hunting  ;  and  is  drawn  as  carrying  a  bow 
and  arrows,  with  a  half  moon  as  an  ornament  on  her  fore- 
head, and  attended  by  several  nymphs  as  her  companions, 
and  by  her  hounds.  She  is  called  also  Phcebe  ;  and  Cyn'- 
thia,  from  having  been  born  on  Mount  Cynthus,  and  she  had 
a  very  famous  temple  at  Eph'esus,  which  is  mentioned  in 
the  New  Testament,  in  the  19th  chapter  of  the  Acts. 

Venus  was  the  goddess  of  beauty  and  of  love ;  and  the 
wife  of  Vulcan,  and  mother  of  Cupid  ;  her  chariot  was 
drawn  by  doves,  and  the  myrtle  was  sacred  to  her.  She 
was  said  to  have  sprung  from  the  sea,  near  the  island  of 
Cythe'ra ;  and  her  most  celebrated  temple  was  at  the  city 
of  Pa'phos,  in  the  island  of  Cyprus  ;  hence  she  is  called  also 
Cythere'a;  and  the  Pa'phian,  or  the  Cyp'rian,  goddess. 
Ves'ta  was  the  goddess  of  the  earth  and  of  fire.  In  her 
temple  at  Rome,  a  perpetual  fire  was  maintainedj  which  was 
kindled  from  the  rays  of  the  sun,  and  was  constantly  watched 
by  priestesses  chosen  from  the  most  noble  families.  They 
were  called  vestal  virgins,  and  had  very  great  honours  and 
privileges.  Ce'res  was  the  goddess  of  corn  and  of  harvest. 
Cyb'ele  was  one  of  the  most  ancient  of  the  goddesses,  being 
the  wife  of  Saturn  ;  and  in  some  respects  represents  the 
earth.  She  is  displayed  as  crowned  with  towers,  holding  a 
key  in  her  hand,  and  drawn  in  her  chariot  by  lions.  Pros'er- 
pine  was  the  wife  of  Pluto,  and  of  course  the  queen  of  the 
infernal  regions.     She  was  the  daughter  of  Ceres.     Amphi- 


ACCOUNT  OF  THE  PRiNCIPAt  HEATHEI^    GODDESSES.    279 

tri'te  was  the  wife  of  Neptune.  Her  sister  was  The'tis, 
another  sea-goddess ;  and  hence,  when  the  sun  sets,  she  is 
said  to  sink  into  Thetis's  lap.  The  foregoing  are  the  prin- 
cipal goddesses. 

Flo'ra  was  the  goddess  of  flowers,  and  Pomo'na  was  the 
goddess  of  fruits.  Belio'na  was  an  inferior  goddess  of  war; 
Aure'ra  was  the  goddess  of  the  morning,  or  rather  of  day- 
break. The'mis,  the  sister  of  Sa'turn,  was  the  goddess  of 
righteousness  and  justice  :  her  daughter  Astre'a  also  repre- 
sents justice  ;  she  is  sometimes  called  the  Virgin,  and  in 
this  character  has  a  place  among  the  stars,  being  denoted  by 
the  constellation  Vir'go,  or  the  Virgin.  Hyge'ia  was  the 
goddess  of  health.  He'be  was  the  goddess  of  youth,  and 
was  cup-bearer  to  Jupiter.  A'te  was  the  goddess  of  mis- 
chief. The  Muses  were  nine  virgin-goddesses  who  pre- 
sided over  every  kind  of  learning,  and  in  that  character  at- 
tended on  Apollo.  They  were  sisters  ;  the  principal  of 
them  were  Cli'o,  who  was  the  muse  of  history  ;  Thali'a,  of 
comedy,  Melpom'ene,  of  tragedy  ;  Terpsic'hore,  of  dancing; 
and  Ura'nia,  of  mathematics  and  astronomy.  They  are 
sometimes  called  merely  the  Nine,  in  reference  to  their 
rmmber. 

Parncis'sus  and  Hel'icon  were  two  mountains  Siicred  to 
Apollo  and  the  Muses;  at  the  feet  of  which  flowed  twa 
streams,  whose  waters  were  supposed  to  communicate  th6 
inspiration  of  prophecy,  or  of  poetry.  Peg'asus  was  a 
winged  horse  of  the  Muses.  The  Graces  were  three  sisters, 
who  were  supposed  to  give  its  attractive  charms  to  beauty 
of  every  kind,  and  to  dispense  the  gift  of  pleasing.  The 
Furies  were  three  sisters  of  a  very  different  character ;  they 
were  the  most  deformed  and  horrible  of  all  the  deities.  In- 
stead of  hair,  they  had  snakes  hanging  from  their  heads. 
They  carried  chains,  and  whips  with  lashes  of  iron  or  of 
scorpions  in  one  hand,  and  lighted  torches  in  the  other. 
They  were  the  bearers  of  the  vengeance  of  heaven.  The 
Destinies  or  Fates,  were  also  three  sisters,  of  whom  One  was 
represented  as  holding  a  distaff;  another  drawing  from  it  a 
thread,  signifying  the  life  of  man  ;  and  the  third  with  a  pair 
of  shears,  ready  to  cut  the  thread  whenever  she  should 
choose.  The  Dry'ads  and  Ham'adryads  were  rural  god- 
desses, each  having  a  single  tree  in  her  charge.  The  Na'- 
iads  were  goddesses  presiding  over  springs,  wells,  and  foun- 


280  HARMONY  OF  SCIENCE  A>'D  CHRISTIANITY. 

tains;  each,  in  the  same  manner,  having  one  under   her 
care.     The  Ne'reids  were  inferior  goddesses  of  the  sea. 
From  Baldwin's  Pantheon. 


LESSON  129. 

Harmony  of  Science  and  Christianity, 

After  all  the  attacks  of  infidelity,  and  of  theoretical  phi- 
losophy, the  religion  of  Christ,  when  contemplated  through 
the  medium  of  science,  has  had  a  complete  and  victorious 
triumph.  It  has  been  often  objected  to  Christianity,  that  it 
is  unfavourable  to  the  progress  of  knowledge ;  that  it  dis- 
courages scientific  enterprises  ;  that  it  is  inimical  to  free 
inquiry,  and  has  a  tendency  to  keep  the  minds  of  men  in 
blindness  and  thraldom.  The  history  of  Christianity,  since 
the  Reformation  at  least,  demonstrates  that  the  very  reverse 
of  what  the  objection  states  is  the  truth.  Christian  nations 
have  been,  of  all  others,  most  remarkable  for  favouring  the 
advancement  of  liberal  knowledge.  In  those  countries  in 
which  religion  has  existed  in  its  greatest  purity,  and  has 
enjoyed  the  most  general  'prevalence,  literature  and  science 
have  been  most  extensively  and  successfully  cultivated.  It 
is  also  worthy  of  remark,  that,  among  all  the  professions  de- 
nominated learned,  the  clerical  profession  may  be  considered 
as  having  furnished  as  many,  if  not  more  authors  of  distinc- 
tion than  any  other.  And  if  we  join  to  the  clergy,  those 
lay  authors  who  have  been  no  less  eminent  as  Christians 
than  as  scholars,  the  predominance  of  learning  and  talents 
on  the  side  of  religion  will  appear  too  great  to  admit  of  com- 
parison. The  discoveries  made  in  mechanical  and  chemical 
philosophy  have  served  to  elucidate  and  confirm  various 
parts  of  the  Christian  Scriptures.  Every  sober  and  well- 
directed  inquiry  into  the  natural  history  of  man,  and  of  the 
globe  we  inhabit,  has  been  found  to  corroborate  the  Mosaic 
history,  and  the  reports  of  voyagers  and  travellers  have 
served  to  illustrate  the  sacred  records,  and  to  confirm  the 
faith  of  Christians.  Never  was  there  a  period  in  which  so 
much  light  and  evidence  in  favour  of  revelation  were  drawn 
from  the  inquiries  of  philosophy  as  in  the  present  era ;  nor 


THE  INFLUENCE  OF  AN  EARLY  TASTE  FOR  READING.  281 

was  it  ever  rendered  so  apparent,  that  the  information  and 
the  doctrines  contained  in  the  sacred  volume  perfectly  har- 
monize with  the  most  authentic  discoveries,  and  the  sound- 
est principles  of  science. 

Questions. — 1.  For  what  have  christian  nations  been  remarkable  ? 
2.  What  is  said  of  the  predominance  of  learning  on  the  side  of  re- 
ligion ?  3.  To  what  purpose  have  discoveries  in  philosophy  been  sub- 
servient ?    4.  What  is  the  character  of  the  present  period  ? 


LESSON  130. 

The  Influence  of  an  early  Taste  for  Reading. 

There  is,  perhaps,  nothing  that  has  a  greater  tendency 
to  decide  favourably  or  unfavourably  respecting  a  man's  fu- 
ture intellect  than  the  question.  Whether  or  not  he  be  im- 
presaed  with  an  early  taste  for  reading. 

Books  are  the  depository  of  every  thing  that  is  most 
honourable  to  man.  He  that  loves  reading  has  every  thing 
within  his  reach.  He  has  but  to  desire,  and  he  may  pos- 
sess himself  of  every  species  of  wisdom  to  judge,  and  power 
to  reform. 

The  chief  point  of  difference  between  the  man  of  talent 
and  the  man  without,  consists  in  the  different  ways  in  which 
their  minds  are  employed  during  the  same  interval  :  they 
are  obliged,  we  will  suppose,  to  walk  from  Temple-bar  to 
Hyde-park  Corner  :  the  dull  man  goes  straight  forward,  he 
has  so  many  furlongs  to  traverse :  he  observes  whether  he 
meets  any  of  his  acquaintance  ;  he  inquires  respecting  their 
health  and  their  family ;  he  glances  his  eye,  perhaps,  at  the 
shops  as  he  passes ;  he  admires,  perchance,  the  fashion  of  a 
buckle,  and  the  metal  of  a  tea-urn.  If  he  experience  any 
flights  of  fancy,  they  are  of  a  short  extent;  of  the  same  na- 
ture as  the  flights  of  a  forest  bird  clipped  of  his  wings,  and 
condemned  to  pass  the  rest  of  his  life  in  a  farm-yard. 

On  the  other  hand,  the  man  of  talent  gives  full  scope  to 
his  imagination.  Unindebted  to  the  suggestions  of  sur- 
rounding objects,  his  whole  soul  is  employed.  He  enters  into 
nice  calculations ;  he  digests  sagacious  reasonings.  In, 
imagination  he  declaims,  or  describes,  impressed  with  the* 
deepest  sympathy  or  elevated  to  the  loftiest  rapture.  He^i 
24  *  ' 


282  THE  MECHANICAL   WONDERS  (TF  A  nEATfCeVt. 

makes  a  thousand  new  and  admirable  combinations.  He 
passes  through  a  thousand  imaginary  scenes,  tries  his  courage, 
tasks  his  ingenuity,  and  thus  becomes  gradually  prepared  to 
meet  almost  any  of  the  many-coloured  events  of  human  life. 
If  he  observes- the  passengers,  he  reads  their  countenances, 
conjectures  their  past  history,  and  forms  a  superficial  notion 
of  their  wisdom  or  folly,  their  virtue  or  vice,  their  satisfac- 
tion or  misery.  If  he  observes  the  scenes  that  oc.cur,  it  is 
with  the  eye  of  an  artist.  Every  object  is  capable  of  suggest- 
ing to  him  a  volume  of  reflections. 

The  time  of  these  two  persons  in  one  respect  resembles; 
it  has  brought  them  both  to  Hyde-park  Corner.  In  every 
other  respect  how  dissimilar  ! 

Probably  nothing  has  contributed  so  much  to  generate 
these  opposite  habits  of  mind,  as  an  early  taste  for  reading. 
Books  gratify  and  excite  our  curiosity  in  innumerable  ways. 
They  force  us  to  reflect ;  they  present  direct  ideas  of  various 
kinds,  and  they  suggest  indirect  ones.  In  a  well-written 
book  we  are  presented  with  the  maturest  reflections,  or  the 
happiest  flights  of  a  mind  of  uncommon  excellence  ;  and  it 
is  impossible  that  we  can  be  much  accustomed  to  such  com- 
panions, without  attaining  some  resemblance  of  them. 

Godwin. 


LESSON  131. 

77ie  Mechanical  Wonders  of  a  Feather. 

LRm'ina  (plural  iaminaB,)  thin  plate,  one  coat  laid  over  another. 
Every  single  feather  is  a  mechanical  wonder.  If  we  look 
at  the  quill,  we  find  properties  not  easily  brought  together, 
strength  and  lightness.  I  know  few  things  more  remarka- 
ble tlian  tlie  strength  and  ligiitness  of  the  very  pen  with 
which  I  am  now  v/riting.  If  we  cast  our  eyes  towards  the 
upper  part  of  the  stem,  we  see  a  material  made  for  the  pur- 
pose, used  in  no  other  class  of  animals,  and  in  no  other  part 
oi'  birds  ;  tough,  light,  pliant,  elastic.  The  pith,  also,  which 
feeds  the  feathers,  is  neither  bone,  flesh,  membrane,  nor 
tendoo.  But  the  most  artificial  part  of  a  feather  is  the  beard^ 
or  as  it  is  sometimes  called,  the  vaiie ;  which  we  usuallj 


THE  MECHANICAL  WONDERS  OP  A  FEATHER.  283 

Strip  off  from  one  side  or  both  when  we  make  a  pen.  The 
separate  pieces  of  which  this  is  composed  are  called  threads, 
filaments,  or  rays^.  Now,  the  first  thing  which  an  attentive 
observer  will  remark  is,  how  much  stronger  the  beard  of  the 
feather  shows  itself  to  be  when  pressed  in  a  direction  per- 
pendicular to  its  plane,  than  when  rubbed  either  up  or  down 
in  the  line  of  the  stem ;  and  he  will  soon  discover,  that  the 
thread  of  which  these  beards  are  composed  are  flat,  and 
placed  with  their  flat  sides  towards  each  other ;  by  which 
means,  while*they  easily  bend  for  the  approaching  of  each 
other,  as  any  one  may  perceive  by  drawing  his  finger  ever 
so  lightly  upwards,  they  are  much  harder  to  bend  out  of  their 
plane,  which  is  the  direction  in  which  they  have  to  encoun- 
ter the  impulse  and  pressure  of  the  air,  and  in  which  their 
strength  is  wanted.  It  is  also  to  be  observed,  that  when  two 
threads,  separated  by  accident  or  force,  are  brought  together 
again,  they  immediately  reclasp.  Draw  your  finger  round 
the  feather  which  is  against  the  grain,  and  you  break,  pro- 
bably, the  junction  of  some  of  the  contiguous  threads  ;  draw 
your  finger  up  the  feather,  and  you  restore  all  things  to  their 
former  state.  It  is  no  common  mechanism  by  which  this 
contrivance  is  eflected  !  The  threads  or  laminae  above  men- 
tioned are  interlaced  with  one  another  ;  and  the  interlacing 
is  performed  by  means  of  a  vast  number  of  fibres  or  teeth 
which  the  threads  shoot  forth  on  each  side,  and  which  hook 
and  grapple  together.  Fifty  of  these  fibres  have  been  count- 
ed in  one  twentieth  of  an  itich.  They  are  crooked,  but 
curved  after  a  different  manner :  for  those  which  proceed 
from  the  thread  on  the  side  towards  the  extremity  of  the 
feather  are  longer,  more  flexible,  and  bent  downward ; 
whereas  those  which  proceed  from  the  side  toward  the  be- 
ginning or  quill-end  of  the  feather,  are  shorter,  firmer,  and 
turned  upward.  When  two  laminse,  therefore,  are  pressed 
together,  the  crooked  parts  of  the  long  fibres  fall  into  the 
cavity  made  by  the  crooked  parts  of  the  others ;  just  as  the 
latch  which  is  fastened  to  a  door,  enters  into  the  cavity  of 
the  catch  fixed  to  the  door-post,  and  there  hooking  itself 
fast<nis  the  door  i  Dr.  Paley. 


284  ART  OF  MAKING  PINS. 

LESSON  132. 

Art  of  Making  Pins.    - 

TuouGH  pins  are  apparently  simple,  their  manufacture 
is,  however,  not  a  little  curious  and  complex.  When  the 
brass  wire,  of  which  the  pins  are  formed,  is  .first  received 
at  the  manufactory,  it  is  generally  too  thicgj^r  the  purpose 
of  being  cut  into  pins.  The  first  operationUJf  efore,  is  that 
of  winding  it  off  from  one  wheel  to  another  vntli  great  velo- 
city, and  causing  it  to  pass  between  the  two,  through  a  circle 
in  a  piece  of  iron  of  smaller  diameter.  The  wire  being  thus 
reduced  to  its  proper  dimensions,  is  straightened  by  drawing 
it  between  iron  pins,  fixed  in  a  board  in  a  zigzag  manner, 
but  so  as  to  leave  a  straight  line  between  them ;  afterwards 
it  is  cut  in  lengths  of  three  or  four  yards^  and  then  into 
5maller  ones,  every  length  being  sufficient  to  make  six  pins. 
Each  end  of  these  is  ground  to  a  point,  which  was  performed, 
when  I  viewed  the  manufactory,  by  boys,  who  sat  each  with 
two  small  grinding-stones  before  him,  turned  by  a  wheel. 
Taking  up  a  handful,  he  applies  the  ends  to  the  coarsest 
of  the  two  stones,  being  careful  at  the  same  time  to  keep 
each  piece  moving  round  between  his  fingers  so  that  the 
points  may  not  become  flat :  he  then  gives  them  a  smoother 
and  sharper  point  by  applying  them  to  the  other  stone,  and 
by  that  means  a  lad  of  twelve  or  fourteen  years  of  age,  is 
able  to  point  about  sixteen  thousand  pins  in  an  hour.  When 
the  wire  is  thus  pointed,  a  pin  is  taken  ofT  at  each  end,  and 
this  is  repeated  till  it  is  cut  into  six  pieces.  The  next  ope- 
ration is  that  of  forming  the  heads,  or,  as  they  term  it,  head- 
spinning,  whicii  is  done  by  means  of  a  spinniiig-wheel,  one 
piece  of  wire  being  thus  with  astonishing  rapidity  wound 
round  another,  and  the  interior  one  being  drawn  out,  leaves 
a  hollow  tube  between  t4ie  circumvolutions  ;  it  is  then  cut 
with  shears,  every  two  circumvolutions,  or  turns  of  the  wire, 
forming  one  head  ;  these  are  softened  by  throwing  them  into 
iron  pans,  and  placing  them  in  a  furnace  till  they  are  red- 
hot.  As  soon  as  they  are  cold,  they  are  distributed  to  chil- 
dren, who  sit  with  hammers  and  anvils  before  them,  which 
they  work  with  their  feet,  by  means  of  a  lathe,  and  taking 
up  oae  of  the  lengths,  they  thrust  the  blunt  ends  into  a 


CLOUDS  AND  RAIN.  385 

quantity  of  the  heads  which  lie  before  them,  and  catching 
one  at  the  extremity,  they  apply  them  immediately  to  the 
anvil  and  hanmier,  and  by  a  motion  or  two  of  the  foot,  the 
top  and  the  head  are  fixed  together  in  much  less  time  than 
it  can  be  described,  and  with  a  dexterity  only  to  be  acquired 
by  practice  ;  the  spectator  being  in  continual  apprehension 
for  the  safety  of  their  fingers'  ends.  The  pin  is  now  finished 
as  to  its  form,  but  still  it  is  merely  brass ;  it  is  therefore 
thrown  into  a  copper  containing  a  solution  of  tin  and  the 
lees  of  wine.  Here  it  remains  for  some  time,  and  when 
taken  out  assumes  a  white,  though  dull  appearance  :  in  or- 
der therefore  to  give  it  a  polish,  it  is  put  into  a  tub  contain- 
ing a  quantity  of  bran,  which  is  set  in  motion  by  turning  a 
shaft  that  runs  through  its  centre,  and  thus  by  means  of  fric- 
tion it  becomes  perfectly  bright.  The  pin  being  complete, 
nothing  remains  but  to  separate  it  from  the  bran,  which  is 
perfectly  similar  to  the  winnowing  of  corn,  the  bran  flying 
off,  and  leaving  the  pin  behind  it  for  immediate  sale. 


LESSON  133. 

Clouds  and  Main. 

Conge'ries,  a  mass  of  small  bodies  heaped  up  together. 

A  CLOUD  is  a  collection  of  vapour,  suspended  in  the  at- 
mosphere. In  other  words,  it  is  a  congeries  of  watery  par- 
ticles raised  from  the  waters,  or  watery  parts  of  the  earth, 
by  the  solar  or  electrical  fire.  These  watery  particles,  in 
their  first  ascent,  arc  too  minute,  and  too  much  separated  by 
their  mutual  repulsion,  to  be  perceived  ;  but  as  they  mount 
higher  and  higher,  meeting  with  a  greater  degree  of  cold, 
losing  their  electricity,  or  by  some  process  employed  by  Na- 
ture for  this  purpose,  they  are  in  a  certain  degree  condensed, 
and  rendered  opaque,  by  the  re-union  of  their  parts^o  as  to 
reflect  and  absorb  light,  and  become  visible  as  clouds. 

The  lowest  part  of  the  air  being  pressed  by  the  weight  of 
the  upper  against  the  surface  of  the  water,  and  continually 
rubbed  upon  it  by  its  motion,  attracts  and  dissolves  those 
particles  with  which  it  is  in  contact,  and  separates  them 
from  the  rest  of  the  water.     And  since  the  cause  of  solution 


286  CLOUDS  AND  RAIN.  \ 

is  the  stronger  attraction  of  the  particles  of  water  towards  j 
the  air  than  towards  each  other,  those  that  are  already  dis-  j 
solved  and  taken  up  will  be  raised  still  higher,  by  the  attrac- 
tion of  the  dry  air,  which  lies  over  them,  and  thus  will  dif-  ' 
fuse  themselves,  rising  gradually  higher  and  higher,  thereby  « 
leaving  the  lower  air  not  so  much  saturated,  but  that  it  will  ] 
still  dissolve  and  take  up  fresh  particles  of  water ;  which  ■ 
process  is  greatly  promoted  by  the  motion  of  the  wind. 

When  the  vapours  are  thus  raised  into  the  higher  and  j 
colder  parts  of  the  atmosphere,  some  of  them  will  coalesce  ; 
into  small  particles,  which,  slightly  attracting  each  other,  : 
and  being  intermixed  with  air,  will  form  clouds ;  and  these  : 
clouds  will  float  at  different  heights,  according  to  the  quan-  j 
tity  of  vapour  borne  up,  and  to  the  degree  of  heat  in  the  up-  \ 
per  part  of  the  atmosphere.  The  clouds,  therefore,  are  ■ 
generally  higher  in  summer  than  in  winter  ;  in  the  former  \ 
season  they  are  from  one  mile  to  three  miles  high,  and  in 
the  latter  from  a  quarter  of  a  mile  to  a  mile.  j 

When  the  clouds  are  much  increased  by  a  continual  ad-  j 
dition  of  vapours,  and  their  panicles  are  driven  close  together  " 
by  the  force  of  the  winds,  they  will  run  into  drops  heavy  • 
enough  to  fall  down  in  rain.  If  the  clouds  are  frozen  be-  | 
fore  their  particles  are  gathered  into  drops,  small  pieces  of  ; 
them  being  condensed,  and  made  heavier  by  the  cold,  they  i 
fall  down  in  flakes  of  snow.  If  the  particles  are  formed  into  • 
drops  before  they  are  frozen,  they  become  hailstones.  When  i 
the  air  is  replete  with  vapours,  and  a  cold  breeze  springs  up  | 
which  checks  the  solution  of  them  in  the  air,  clouds  are  | 
formed  in  the  lower  parts  of  the  atmosphere,  and  these  com-  '. 
pose  a  mist  ox  fog :  this  usually  happens  in  a  cold  morning  ;  ; 
but  the  mist  is  dispersed  when  the  sun  has  warmed  the  air,,  \ 
and  made  it  capable  of  dissolving  the  watery  particles  of  ' 
which  the  mist  is  composed. 

Southerly  winds  generally  bring  rain,  because,  being  J 
commonly  warm,  and  replete  with  aqueous  vapours,  they  are  ] 
cooled  by  passing  into  a  colder  climate  ;  and  therefore  part  | 
with  some  of  them,  and  suffer  them  to  precipitate  in  rain :  ' 
northerly  winds,  on  the  contrary,  being  cold,  and  acquiring  I 
heat  by  coming  into  a  warm  climate,  take  up  or  dissolve  I 
more  vapour  than  they  before  contained  ;  and  ttierefore  are  } 
dry  and  parching,  and  usually  attended  with  fair  weather.       • 

Gregory. 


ART  OP  PRINTING.  287 

Questions. — 1.  What  is  a  cloud?  2.  Describe  the  process  by 
which  the  watery  particles  are  supposed  to  become  visible  clouds. 
3.  What  is  the  process  by  which  other  or  fresh  particles  of  water  are 
taken  up  ?  4.  Why  are  clouds  generally  higher  in  summer  than  in 
winter  ?  5.  When  will  clouds  fall  down  in  rain  ? — in  flakes  of  snow  ? 
6.  When  do  they  become  hailstones  ?  7.  How  and  when  is  mist  or 
fog  produced  ?  8.  Why  do  southerly  winds  generally  bring  rain  ?  9. 
Why  are  north  winds  usually  attended  with  fair  weather. 


LESSON  134. 

Invention  and  Progress  of  Printing. 
Glu'tinous,  gluey,  viscous,  tenacious. 

The  art  of  printing  deserves  to  be  considered  with  atten- 
tion and  respect.  From  the  ingenuity  of  its  contrivance,  it 
has  ever  excited  mechanical  curiosity  ;  from  its  intimate 
connexion  with  learning,  it  has  justly  claimed  historical  no^ 
tice  ;  and  from  its  extensive  influence  on  morality,  politics, 
and  religion,  it  is  now  become  a  very  important  speculation. 
Coining,  and  taking  impressions  in  wax,  are  of  great  antiqui- 
ty, and  the  principle  is  precisely  that  of  printing.  The  ap- 
plication of  this  principle  to  the  multiplication  of  books, 
constituted  the  discovery  of  the  art  of  printing.  The  Chi- 
nese have  for  many  ages  printed  with  blocks,  or  whole  pages 
engraved  on  wood ;  but  the  application  of  single  letters  or 
moveable  types  forms  the  merit  of  the  European  art. 

The  honour  of  giving  rise  to  this  method  has  been  claimed 
by  the  cities  of  Harlem,  Mentz,  and  Strasburg ;  and  to  each 
of  these  it  may  be  ascribed  in  some  degree,  as  printers  resi- 
dent in  each  made  successive  improvements  in  the  art. 

It  is  recorded  by  a  reputable  author,  that  Laurens  Rosier 
of  Harlem,  walking  in  a  w^ood  near  that  city,  cut  some  letters 
upon  the  rind  of  a  beech-tree,  which  for  fancy's  sake,  being 
impressed  upon  paper,  he  printed  one  or  two  lines  for  his 
grand-children  ;  and  this  having  succeeded,  he  invented  a 
more  glutinous  ink,  because  he  found  the  common  ink  sunk 
and  spread  ;  and  then  formed  wliole  pages  of  wood,  with 
letters  cut  upon  them,  and  (as  nothing  is  complete  in  its 
first  invention)  the  backsides  of  the  pages  were  pasted  to- 
gether, that  they  might  have  the  appearance  of  manuscripts 
vrritten  on  both  sides  of  the  paper.     These  beechen  letters 


liQS  HOPE. 

he  afterwards  exchanged  for  leaden  ones,  and  these  again 
for  a  mixture  of  tin  and  lead,  as  a  less  flexible  and  more 
solid  and  durable  substance.  He  died  in  1440,  and  by  some 
his  first  attempt  is  supposed  to  have  been  made  about  1430, 
but  by  others  as  early  as  1423. 

From  this  period  printing  made  a  rapid  progress  in  most 
of  the  principal  towns  of  Europe,  superseded  the  trade  of 
copying,  which,  till  that  time,  was  very  considerable,  and 
was  in  many  places  considered  as  a  species  of  magic.  In 
1490  it  reached  Constantinople,  and  was  extended  by  the 
middle  of  the  following  century  to  Africa  and  America. 

During  the  period  since  its  invention,  what  has  not  the 
art  of  printing  effected  ?  It  has  blunted  the  edge  of  perse- 
cution's sword,  laid  open  to  man  his  own  heart,  struck  the 
sceptre  from  the  hand  of  tyranny,  and  awakened  from  its 
slumber  a  spirit  of  knowledge,  cultivation,  liberty.  It  has 
gone  forth  like  an  angel  scattering  blessiiigs  in  its  path,  so- 
lacing the  wounded  mind,  and  silently  pointing  out  the  tri- 
umphs of  mortality  and  the  truths  of  revelation  to  the  gaze 
of  those  whom  the  want  of  precept  or  good  example  had  de- 
based, and  whom  ignorance  had  made  skeptical. 

Questions. — 1.  The  applica*ion  of  what  principle  to  the  multipK- 
cation  of  books  constitutes  thn' discovery  of  the  art  of  printing  ?  2. 
What  is  said  of  Harlem,  Mentz,  and  Strasburg  ?  3.  What  is  related 
of  Laurens  Koster  ?  4.  What  is  said  of  the  progress  of  printing  in 
the  world?  5.  Of  its  effects?  [Note.  The  fourth  Centennial  Anni- 
versary of  the  Inventi6n  of  Printing  was  observed  at  Harlem  in  Hol- 
land on  tiie  10th  and  11th  of  July,  1823,  with  great  rejoicing  and  a 
«pl«ndid  festival.] 


LESSON  135. 

Hope. 

There  is  no  happiness  which  hope  cannot  promise, — no 
difficulty  which  it  cannot  surmount, — no  grief  which  it  can- 
not mitigate.  It  is  the  wealth  of  the  indigent,  the  health 
of  the  sick,  the  freedom  of  the  captive.  As  soon  as  we  have 
learned  what  is  agreeable,  it  delights  us  with  the  prospect 
of  attaining  it ;  as  soon  as  we  have  lost  it,  it  delights  us 
^vitli  the  prospect  of  its  return.     It  is  our  flatterer  and  com» 


HOPE.  289 

forter  in  youth ;  it  is  our  flatterer  and  comforter  in  years 
which  need  still  more  to  be  flattered  and  comforted.  What 
it  promises,  indeed,  is  different  in  these  different  years  ;  but 
the  kindness  and  irresistible  persuasion  with  which  it  makes 
the  promise  are  still  the  same  ;  and  while  we  laugh,  in  ad- 
vanced age,  at  the  easy  confidence  of  our  youth  in  wishes 
which  seem  incapable  of  deceiving  us  now,  we  are  still,  as  to 
other  objects  of  desire,  the  same  credulous,  confiding  beingSj 
whom  it  was  then  so  easy  to  make  happy.  Nor  is  it  only 
over  terrestrial  things  that  it  diffuses  its  delightful  radiance. 
The  power  which  attends  us  with  consolation,  and  with  more 
than  consolation,  through  the  anxieties  and  labours  of  our 
life,  does  not  desert  us  at  the  close  of  that  life  which  it  has 
blessed  or  consoled.  It  is  present  with  us  in  our  last  mo- 
ment. We  look  to  scenes  which  are  opening  on  us  above, 
and  we  look  to  t^ose  around  us,  with  an  expectation  still 
stronger  than  the  strongest  hope,  that,  in  the  world  which 
we  are  about  to  enter,  we  shall  not  have  only  remembrances 
of  what  we  loved  and  revered  on  earth,  but  that  the  friend- 
ships from  which  it  is  so  painful  to  part,  even  in  parting 
to  Heaven,  will  be  restored  to  us  there,  to  unite  us  again  in 
affection  more  ardent,  and  in  still  purer  adoration  of  that 
Great  Being,  whose  perfections,  as  far  as  they  were  then 
dimly  seen  by  us,  it  was  our  delight  to  contemplate  together 
on  earth,  when  it  was  only  on  earth  that  we  could  trace 
them,  but  on  that  earth  which  seemed  holier,  and  lovelier, 
and  more  divine,  when  thus  joined  in  our  thought  with  the 
Excellence  that  made  it.  Browne 

25 


APPENDIX. 


EXPLANATION  OF  THE  ENGRAVINGS. 

LESSON  17. 

Centre  of  Gravity.  Engraving  I. — If  the  centres  of  gra- 
vity^ of  two  bodies,  A  and  B,  fig.  12.  be  connected  with  the 
right  line  A  B,  then  the  common  centre  of  gravity,  C,  will  be 
as  much  nearer  to  A  than  to  B,  as  the  ball  A  is  heavier  than 
the  ball  B.  If  the  ball  A  weigh  12  pounds,  and  the  ball  B  only 
4  pounds,  and  the  length  A  B  be  20  inches,  then,  because  the 
ball  A  is  three  times  heavier  than  the  ball  B,  the  distance 
A  C  will  be  three  times  less  than  the  distance  B  C,  that  is, 
A  C  will  be  5  inches  and  B  C  15  inches ;  the  point  C,  there- 
fore, is  the  common  centre  of  gravity  of  the  two  bodies  A 
and  B,  and  if  supported  by  this  point  they  will  balance  each 
other.  As  12-|-4=:16  is  to  20,  so  is  4  to  5,  or  so  is  12 
to  15. 

The  inclining  body  A  B  C  D,  fig.  4.  whose  centre  of  gra- 
vity is  E,  stands  firmly,  because  the  line  of  direction  E  F 
falls  within  the  base.  But  if  the  body  A  B  G  H  be  placed 
upon  it,  the  centre  of  gravity  will  be  raised  to  L,  and  then 
the  line  of  direction  L  D  will  fall  out  of  the  base  towards  I : 
the  centre  of  gravity,  therefore,  is  not  supported,  and  thQ 


whole  body  must  fall. 


LESSON  19. 


Compound  Motion. — The  body  A,  fig.  1.  acted  upon  by  a 
force  in  the  direction  A  B,  and  at  the  same  time  by  another 
force  in  the  direction  A  C,  will  move  in  the  direction  A  D. 
If  the  lines  A  B  and  A  C  be  made  in  proportion  to  the 
forces,  and  C  D  and  D  B  be  drawn  parallel  to  them,  then 
A  D,  the  diagonal,  will  represent  the  force  with  which  the 
body  will  move  ;  and  this  force  will  be  as  much  greater  than 
either  of  the  two  forces  by  which  it  was  impelled  as  A  D  is 


"  A1»PEND1X.  291 

longer  than  A  C,  or  any  other  single  side  of  the  parallelo- 
gram. This  is  called  the  composition  and  resolution  of  mo- 
tion. [Note.  Several  things  in  this  Lesson  may  be  obscure 
to  some  students :  the  teacher  should  explain  and  illustrate 
them  by  familiar  "  verbal  instructions,"  and  by  such  figures 
and  diagrams  as  he  may  have  in  his  possession,  or  may 
easily  draw  upon  paper  or  a  slate.] 

LESSON  20. 

Levers. — First  kind,  ^g.  7.  C  E  is  the  lever,  and  B  the 
prop.  A  the  stone  to  be  raised  =  1000  pounds,  and  the 
strength  of  a  man  at  C  =  100  pounds.  Since  the  strength 
of  the  man  is  only  one  tenth  the  weight  of  the  stone,  that  the 
power  and  weight  may  balance  each  other,  the  arm  of  the 
lever  B  C  must  be  ten  times  as  long  as  the  arm  B  E.  Second 
kind,  fg.  9.  If  the  hand  C  be  nine  times  as  far  from  A  as 
the  point  X,  then  one  pound  at  C  will  balance  nine  pounds 
at  B.  Fig-  5.  a  burden  on  a  pole.  Weight  W  three 
times  nearer  to  a  than  to  b,  a  then  will  bear  three  times  as 
much  of  the  weight  as  b.  Third  kind,  Jig.  10.  Distance 
P  F  3  inches  ;  W  F  12  :— then  20  pounds  at  W  will  require 
the  force  of  80  at  P  in  order  to  balance  it,  for  12  is  four 
times  3.  Fig.  2.  man's  arm, — D  centre  of  motion, — the 
power  is  the  muscle  inserted  at  C, — A  the  weight : — now  as 
the  distance  D  C  is  one  tenth  part  of  C  A,  the  muscle,  there- 
fore, must  exert  a  power  equal  to  100  pounds  in  order  to 
raise  10  pounds. 

LESSON  21. 

Pulley. — Fig.  13.  single  moveable, — in  order  to  raise  the 
weight  W  one  inch,  the  power  P  must  draw  the  strings  B 
and  C  one  inch  each  :  the  whole  string,  therefore,  is  short- 
ened two  inches,  while  the  weight  is  raised  only  one.  Fig. 
15.  System  of  pullies.  While  the  weight  W  rises  one  inch, 
each  of  the  four  ropes  must  be  shortened  an  inch,  and  P, 
therefore,  must  move  four  inches  :  5  pounds  at  P  will  ba- 
lance 20  at  W.  Wheel  and  Axle,  Fig.  11.  If  the  diame- 
ter of  the  wheel  be  4  feet,  and  that  of  the  axis  only  8  inches, 
then  the  power  P  of  100  pounds  will  balance  the  weight  W 
of  600  pounds  ;  for  6x8=48  inches  which  make  4  feet,  the 
diameter  of  the  wheel.     Inclined  Plane.  Fig.  8.  If  B  C= 


m 


292  APPENDIX. 

4  A  C,  then  W  will  be  supported  by  a  power  =  }  of  its 
weight.  Example.  If  a  wagon  with  its  load  weigh  40  cwt. 
and  may  be  drawn  on  level  ground  by  a  force  equal  to  8 
cwt,  in  drawing  it  to  the  top  of  a  hill  which  rises  20  yds. 
in  a  XOO,  the  horses  will  have  to  pull  with  an  additional 
force  =3  i  of  40  cwt.,  that  is,  8  cwt.  more  than  on  level 
ground,  or  with  double  their  former  force. 

LESSON  22. 

T/ie  Wedge,  Jig.  6. — A  BCD  may  be  divided  into  two 
inclined  planes,  ADC  and  B  D  C,  which  may  be  used  se- 
parately, and  will  gain  advantage  as  such  ;  therefore,  when 
united  at  D  C,  the  advantage  gained  will  be  in  the  same  pro- 
portion as  when  they  were  used  in  different  parts.  The 
Screw,  jig.  3.  A  must  turn  once  round  before  the  resistance 
can  be  moved  from  one  spiral  winding  to  another,  as  from  x 
to  z  =  ^  an  inch.  If  the  lever  A  :=:  36  inches,  then  the 
circle  described  by  its  end  a  will  be  about  226  inches  or 
452  half  inches;  therefore  one  pound  at  «  will  balance  a 
resistance  of  452  pounds,  [Note.  Since  the  lever  m  36 
inches,  the  diameter  of  the  circle  will  be  72  inches,  and  the 
circumference  of  a  circle  is  3.1416  times  the  diameter,  there- 
fore, 72x3.1416  z=L  the  circumference  z=z  226  inches  or  452 
half  inches.] 

LESSON  23. 

Pressure  of  Fluids. — In  the  vessel  A  B,  Jig.  25.  Engr. 
II.  the  bottom  C  B  does  not  sustain  a  pressure  equal  to  the 
quantity  of  the  whole  fluid,  but  only  of  a  column,  whose  base 
is  C  B,  and  height  C  F.  In  the  vessel  F  G,/^.  24.  the  bot- 
tom sustains  a  pressure  equal  to  what  it  would  if  the  vessel 
were  as  wide  at  the  top  as  bottom.  If  to  the  wide  vessel 
A  B,  Jig.  23.  a  tube  C  D  be  attached,  and  water  poured  into 
either  of  them,  it  will  stand  at  the  same  height  in  both ;  of 
course  the  small  quantity  in  C  D  balances  the  large  quantity 
in  A  B.  This  has  been  called  the  hydro  statical  paradox, 
because  any  quantity,  hoicevcr  small,  may  be  made  to  coun- 
terpoise any  quantity,  however  large,  but  it  is  no  paradox,  when 
we  consider  that  the  particles  of  a  fluid  press  against  each 
other  in  every  direction,  not  only  downwards,  but  upwards 
and  sideways. 


APPENDIX.  293 


LESSON  24 

Specific  Gravity.  Hydrostatic  Balance,  fig.  14.  Engr.  I. 
If  a  body  x,  suspended  under  the  scale,  be  first  counterpois- 
ed in  air  by  weights  in  the  opposite  scale,  and  then  im- 
mersed in  water,  the  equilibrium  will  be  destroyed,  then  if 
a  weight  be  put  into  the  scale  from  which  the  body  hangs, 
to  restore  the  equilibrium,  that  weight  will  be  equal  to  the 
weight  of  water  as  large  as  the  immersed  body, — or  it  is 
what  the  body  loses  of  its  weight  in  the  fluid. 

The  Hydrometer  consists  of  a  thin  glass  ball,  with  a  gra- 
duated tube  :  a  smaller  ball  is  attached  to  the  instrument 
below,  containing  a  little  mercury,  for  the  purpose  of  making 
it  remain  upright  in  the  liquid  under  trial.  The  specific 
gravity  of  the  liquid  is  estimated  by  the  depth  to  which  the 
instrument  sinks. 

LESSON  25. 

The  Common  Pump,  fig.  2L  Engr.  IL  AB  the  barrel. 
P  the  piston.  R  the  rod.  V  the  valve  in  the  moveable  pis- 
ton, y  a  valve  fixed  in  the  body  of  the  pump.  S  the  spout. 
The  Forcing  Pump,  fig.  22.  A  B  the  barrel.  P  a  solid 
piston.  D  the  pipe  joined  to  the  barrel.  V  a  fixed  valve. 
When  P  descends  it  shuts  the  valve  y,  and  forces  the  water 
into  D  through  V.  When  P  is  raised  the  valve  y  opens  and 
the  valve  V  shuts,  and  the  water  ascends  through  y.  The 
forcing  pump  described  in  the  Lesson  differs  a  little  from 
this  figure.  We  may  suppose  an  air  vessel  to  be  placed 
above  V,  and  a  pipe  descending  through  it  nearly  to  V,  and 
the  elastic  pressure  of  the  air  upon  the  surface  of  the  water, 
confined  in  the  vessel,  will  force  the  water  upwards  through 
the  pipe. 

LESSON  27. 

The  Air  Pump,  fig.  16.  D  E  the  base  or  wooden  frame. 
A  A  the  two  brass  cylinders.  B  the  head.  C  C  the  co- 
lumns holding  down  the  head.  K  the  receiver.  I  a  hole 
in  the  brass  plate,  through  which  the  air  passes  in  a  brass 
tube  to  the  cylinders.  R  R  toothed  rods.  H  handle  or 
winch.  N  a  nut,  on  turning  which  the  air  may  be  excluded 
25* 


S94 


APPENDIX. 


from,  or  admitted  to  the  receiver.     M  a  quicksilver  gage  ^ 

with  a  small  receiver  over  it :  this  is  designed  to  show  the  ^ 

different  densities  of  the  air  in  the  large  receiver,  when  the  i 
machine  is  at  work.     There  is  a  communication  between 

this  and  the  hole  I  by  a  brass  pipe.     This  is  not  an  essen-  ^ 
tial  part  of  an  air  pump,  though  it  is  convenient,  as  showing 

the  degree  of  exhaustion  :  the  more  the  air  is  exhausted  the  ■ 

higher  will  the  mercury  rise  in  the  gage.  ? 

Artificial  Fountain,  jig.  26.     A  is  a  strong  copper  vessel,  '* 

having  a  tube  that  screws  into  the  neck  of  it,  so  as  to  be  air  i 

tight,  and  so  long  as  nearly  to  reach  to  the  bottom  :  x  is  the  \ 

handle  of  a  stop.     Having  poured  some  water  into  the  ves-  ; 

sel,  and  screwed  in  the  tube,  the  condensing  syringe  is  to  be  \ 

adapted,  and  the  air  condensed.     The  stop  is  to  be  shut  \ 

while  the  syringe  is  unscrewed,  then,  on  opening  the  stop,  • 

the  air,  by  its  great  density  acting  upon  the   v/ater  in  the  ■ 
Yessel,  will  force  it  out  in  a  jet  to  a  considerable  height, 

LESSON  29.  1 

Sound.  Speaking  Trumpet,  Jig.  20.  The  voice  instead  i 
of  being  diffused  in  the  open  air,  is  confined  within  the  j 
trumpet,  and  the  vibrations  which  spread  and  -fall  against  ; 
the  sides  of  the  instrument,  are  reflected  according  to  the 
angle  of  incidence,  and  fall  into  the  direction  of  the  vibra-  \ 
tions  which  proceed  straight  forwards.  The  wliole  of  the  J 
vibrations  are  thus  collected  into  a  focus,  and  if  the  ear  be  \i 
situated  in  or  near  the  spot,  the  sound  is  prodigiously  in-  > 
creased.  The  reflected  rays  are  distinguished  from  those  ] 
of  incidence,  by  being  dotted,  and  they  are  brought  to  a  ? 
focus  at  F.       "  \ 

LESSON  30.  i 

Musical  Sounds. — The  line  A  B,  Jig.  17.  represents  a  ; 
musical  string  fastened  at  both  ends.  Drawn  out  in  the  -| 
situation  A  C  B,  and  then  let  go,  it  will,  in  consequence  of  ; 
its  elasticity,  not  only  come  back  to  its  position  A  B,  but  go  ^ 
to  the  situation  A  D  B,  or  nearly  as  far  from  A  B  as  A  C  B  : 
was  on  the  other  side.  All  the  motion  one  way  is  called  one  j 
vibration  ;  after  this,  the  string  will  go  again  nearly  as  far  ^ 
a;6  C,  making  a  second  vibration,  then  nearly  as  far  as  D,  1 
making  a  third  vibration,  and  so  on,  diminishing  the  extent 


APPENDIX.  295 

of  its  vibrations  gradually,  until  it  settles  again  in  its  origi- 
nal position  A  B.  According  to  the  laws  of  pendulums, 
those  of  equal  length  move  in  equal  times,  though  they  pass 
through  difterent  arcs,  or  portions  of  a  circle.  If  the  pen- 
dulums AB,  fig.  18.  and  C  D,  fig.  19.  be  equal,  the  time  of 
passing  through  EF  is  equal  to  that  of  passing  through  G  H. 
Thus  the  vibration  of  the  string  AB,  fig.  17.  is  considered 
as  a  double  pendulum,  vibrating  from  the  points  A  and  B, 
the  respective  vibrations  of  which,  from  the  greatest  to  the 
least,  are  performed  in  the  same  time  :  this  is  the  reason 
why  a  musical  string  has  the  same  tone  from  the  beginning 
of  the  vibrations  to  the  end. 

LESSON  8L 

Optics.  Rejicction  and  Refraction  of  Light.  If  L  G^ 
fig.  29.  Engr.  III.  be  a  reflecting  surface,  as  a  looking  glass, 
then  B  C  is  the  incideiit  ray,  and  C  E  is  the  reflected  ray. 
The  line  F  C  is  a  perpendicular  to  the  reflecting  surface 
L  G.  The  angle  of  incidence  is  that  which  is  contained 
between  B  C  and  C  F,  and  the  angle  of  reflection  is  that 
contained  between  E  C  and  C  F  :  and  the  angle  of  incidence 
is  equal  to  the  angle  of  reflection,  that  is,  the  angle  B  C  F 
is  equal  to  the  angle  E  C  F.  (It  is  usual  to  call  every  angle 
by  three  letters,  and  that  at  the  angular  point  must  be  always 
the  middle  letter  of  the  three.) 

Let  B  C,  fig.  29.  be  a  ray  of  light  passing  out  of  air  into 
water  or  glass  L  G  at  the  point  C,  the  ray  B  C,  instead  of 
proceeding  along  C  H,  will  be  bent,  or  refracted  towards  the 
perpendicular  C  K,  as  along  C  I.  But  if  C  I  be  supposed  to 
be  a  ray  of  light  passing  out  of  glass  or  water  into  air,  that 
is,  out  of  a  denser  into  a  rarer  medium,  it  will  not  proceed 
in  the  direction  of  the  line  C  x,  but  in  the  direction  C  B, 
farther  from  the  perpendicular  F  C  than  C  x,  [Note.  On 
the  subject  of  optics  the  instructer  should  be  particular  in 
giving  his  pupils  a  correct  idea  of  angles,  parallel  lines,  &c.] 

LESSON  32. 

Lenses.  Fig.  3Q.  A  is  a  plano-convex  lens,  B  plano- 
concave, C  double  convex,  D  double  concave,  E  a  meniscus. 
F  G  is  the  axis  of  all  the  five  lenses. 

Fig.  36.     A  candle  at  C  diverges  rays  of  light  towardi  ar» 


2U6 


APPENDIX 


They  are  said  to  converge  when  considered  as  flowing  from 
X  towards  C.  And  to  be  parallel  as  flowing  from  x  towards 
a  and  h.  C  i^  the  focus  of  the  converging  rays,  and  the 
imaginary  focus  of  the  diverging  rays.  The  lens  here  being 
plano-convex,  the  focus,  as  is  manifest,  is  at  the  distance  of 
the  diameter  of  the  sphere,  of  which  the  convex  surface  of 
the  lens  forms  a  portion.  The  distance  from  the  middle  of 
the  glass  to  the  focus  is  called  tlie  focal  distance. 

Fig.  32.  The  focal  distance  of  a  double  convex  lens  is 
situated  at  the  centre  of  the  sphere,  of  which  the  surface  of 
the  lens  forms  a  portion  ; — of  the  lens  A  B,  for  instance,  f 
is  the  focus,  and  the  distance  from  f  to  the  circumference 
of  the  circle  is  the  focal  distance,  which  is  equal  to  half  the 
diameter  of  the  sphere.  If  another  double  convex  lens  FG 
be  placed  in  the  rays  at  the  same  distance  from  the  focus,  it 
will  so  refract  the  rays,  that  they  shall  go  out  of  it  parallel  to 
one  another.  It  is  evident  that  all  the  rays  except  the  mid- 
dle one,  cross  each  other  in  the  focus  /;  of  course  the  ray 
D  A,  which  is  uppermost  in  going  in,  is  the  lowest  in  going 
out,  as  G  c. 

Pig.  33.  If  the  rays  ahc,  &lc.  pass  through  A  B,  and  C 
be  the  centre  of  concavity,  then  the  ray  a,  after  passing 
through  the  glass,  will  go  in  the  direction  Ic  I,  as  if  it  had 
come  from  C,  and  no  glass  in  the  way  :  the  ray  b  will  go  on 
in  the  direction  wM,,and  so  on.  The  point  C  is  called  the 
imaginary  focus, 

LESSON  33. 

In  fig.  27.  A  B  is  a  concave  mirror,  C  is  the  centre  of 
concavity.  The  rays,  which  proceed  from  any  remote  terres* 
trial  object,  as  D  E,  will  be  converged  at  a  little  greater  dis- 
tance than  half  way  between  the  mirror  and  C,  and  the 
image  will  be  inverted  with  respect  to  the  object,  as  de. 
When  the  object  is  more  remote  than  the  centre  of  concavi- 
ty, or  C,  the  image  is  less  than  the  object,  and  is  between 
the  object  and  the  mirror,  as  J  e  between  D  E  and  B  C. 
When  the  object  is  nearer  than  C,  the  image  will  be  more 
remote  and  larger  than  the  object,  as  D  E.  If  the  object  be 
in  C,  the  image  and  object  will  be  equal  and  coincide. 


APPENDIX.  29? 

LESSON  34. 

Fig.  37.  P  is  a  prism.  A  is  a  ray  of  light,  which  is  re- 
fracted on  entering  the  prism,  and  also  on  leaving  it.  A  B 
is  the  spectrum,  on  which  are  exhibited  the  variously  colour- 
ed rays. 

LESSON  36. 

Structure  of  the  Eye.  Fig.  28.  aaaaa,  is  called  the 
sclerotica :  h  b,  the  cornea :  c  cc,  the  choroid :  d  d,  the  pu- 
pil :  e  e,  the  iris :  ff,  the  aqueous  humour :  g  g,  the  cri/s- 
talline  humour  :  h  h,  the  vitreous  humour  :  i  i,  the  retina  ; 
which  proceeds  from  the  brain  and  enters  the  eye  at  n. 

LESSON  37. 

Single  Microscope,  Jig.  35.  E  F  is  the  object  to  be  view* 
ed  :  A  B  a  double  convex  lens :  c  the  pupil  of  the  eye :  D 
the  crystalline  humour  :  the  rays  are  converged  to  a  focus  on 
the  retina  at  R  R.  Compound  Microscope,  Jig.  34.  with 
which  we  do  not  see  the  object  A  B,  but  a  magnified  image 
of  it  a  h.  Two  lenses  are  employed  ;  the  one  L  M,  for  the 
purpose  of  magnifying  the  object,  is  called  the  object  glass  : 
the  other  N  O,  acts  on  the  principle  of  the  single  micro- 
scope, and  is  called  the  eye  glass. 

LESSON  39. 

To  obtain  an  idea  of  the  Newtonian  Telescope,  look  at 
jig.  27.  ai»d  consider  the  concave  mirror  A  B  as  placed  at 
the  end  of  a  tube,  and  rays  of  light  falling  upon  it  from  the 
object  DE  :  then  suppose  a  plane  mirror  placed  a  little  be- 
low e,  so  that  the  rays,  being  reflected  from  it,  shall  pass  out 
through  a  lens  at  d,  where  the  eye  of  the  observer  looks 
down  on  the  image. 

LESSON  4L 

Solar  System.  Engr.  IV.  Fig.  38  exhibits  the  order  in 
which  the  planets  move  round  the  sun.  Fig.  39  shows 
their  comparative  magnitudes.  On  the  left  hand  side  of  the 
Engr.  are  represented  the  proportional  distances  of  the 
olanets  from  the  sun. 


298 


APPENDIX. 

LESSON  42. 


Table  of  the  distances,  rotations,  periods,  &c.  of  the 
Sun  and  Planets. 


$ 

i-H 

GO 

i 

§ 

o 

to 

§ 

to 

g 

o 

i 

2 

i 

t2 

Greatest 
distance 
from  the 
Ecliptic. 

0 

t 

o 

o 
o 

g. 

2 

b 

CO 

o 
o 

2 

o 

o 

-k 

(M 

'I'* 

pH 

'-i: 

-id 

S 
3 

3 

_s 

3 

0>|c 

H«5 

iarth  beiog 

Heat  and 
Light. 

s 

o 

5 
1— r 

CO 

QO 

-<* 

CO 

CO 

o 

i 

Thel 
Bulk. 

1 

l"2 

"1- 

* 

»*^ 

1^ 

3 

~!c. 

1- 

-1? 

* 

-^ 

2 

o 
o 
o 

1— ( 

i 

£  S 
Q-2 

i^ 

1 

CO 

1^ 

CO 

Ci 

i 

3 

* 

* 

1 

* 

? 

i 

o 

Hi 

43 

i 

CO 

CD 

e 

a 

3 

* 

"c 

^ 
c 

2 

c 

s 

3 

Time  of 

revolving 

round  the 

sun. 

-d 

olo 

CO 

o 

2 

CO 

o 

o 

o 

CO 
CO 

s 

GO 

Dis- 
tance 
in  Mill- 
ions. 

s 

s 

s 

rf 
^ 

CO 

CO 

i 

i 

1 

i 

1-H 

c 

5 

i 
> 

1 

s! 

> 

o 

J 

IB 

1 

2 

i 
1 

i 

t5 

Note.  The  planets  receive  light  and  heat  from  the  sun 
according  to  the  square  of  their  distances,  that  is,  light  and 
heat  decrease  as  the  jgquare  of  the  distance  increases.  If  the 
distance  of  one  planet  be  called  1,  of  another  2,  and  of  a  third 
3,  the  heat  and  light  received  at  the  first  is  1x1=1,  at  the 
second  3x2=:4  times  less,  or  i,  at  the  third  3x3=9  times 


APPENDIX.  299 

less,  or  1.  The  following  rule  may  be  given ;  as  the  square 
of  the  distance  of  any  planet  from  the  sun  is  to  I,  which  re- 
presents the  light  and  heat  received  at  the  earth,  so  is  the 
square  of  the  earth's  distance  from  the  sun,  to  the  degree  of 
light  and  heat  received  at  the  planet  in  question. 

The  attraction  of  bodies  dexreases  as  the  square  of  the  dis- 
tance increases ;  the  attraction  is  mutual,  and  greater  or  less 
according  to  their  solid  contents. 

The  following  is  the  rule  for  finding  the  distances  of  the 
planets  from  the  sun  : — as  the  square  of  the  earth's  period  of 
revolution  round  the  sun  is  to  the  cube  of  its  disC-^nce,  so  is 
the  square  of  any  other  planet's  annual  period  of  revolution 
to  the  cube  of  its  distance  ;  and  the  cube  root  of  the  number 
thus  found  will  be  the  planet's  distance  from  the  sun.  It 
was  ascertained  by  Kepler  and  demonstrated  by  Newton, 
that  from  the  combined  forces  of  attraction  and  rectilinear 
motion,  the  squares  of  the  periodical  times  or  revolutions  of 
the  planets  are,  as  the  cubes  of  their  distances.  It  was  as- 
certained by  Kepler  also,  that  if  a  line  were  drawn  from  the 
sun  to  the  earth,  this  line  would,  by  the  earth's  motion,  pass 
over  equal  spaces,  or  areas  in  equal  times. 

To  such  pupils  as  are  sufficiently  acquainted  with  Arith- 
metic, the  instructor  should  explain  at  large  the  particulars 
mentioned  in  the  above  note.  Questions  may  easily  be  pro- 
posed, and  worked  out  by  the  above  rules : — for  instance,  if 
the  period  of  Mercury  be  88  days,  what  is  its  distance  from 
the  sun  1 — If  the  heat  and  light  at  the  earth  be  1,  what  is  the 
degree  of  heat  and  light  at  Mercury?  and  so  of  other  planets. 

To  find  how  many  times  one  planet  is  greater  than  ano- 
ther, the  rule  is,  cube  the  diameter  of  each  planet,  and  di- 
vide the  greater  number  by  the  less,  the  quotient  will  give  the 
proportional  magnitudes,  or  the  number  of  times  the  one  is 
greater  than  the  other. 

LESSON  44. 

Fig.  40.  Engraving  V.  S  represents  the  sun,  and  N  S  is 
the  earth  in  different  parts  of  its  orbit.  The  white  circle  in 
the  dark  space  represents  the  ecliptic.  The  dark  circular 
space  filled  with  stars  extending  eight  degrees  from  each 
side  of  the  ecliptic  represents  the  zodiac.  The  names  of 
the  signs  of  the  zodiac  and  the  characters  which  represent 


yOO  APPENDIX. 


them  are  placed  around  the  zodiac,  as  Aries,  Taurus,  &.c. 
At  March  20th,  the  earth  as  seen  from  the  sun  appears  at    | 
the  beginning  of  the  sign  Libra;  but  the  sun  as  seen  from 
the  earth,  at  that  time,  appears  at  the  beginning  of  the  sign    ^ 
Aries.     Some  of  the  particulars  mentioned    in    Lesson  44  ■\ 
should  be  illustrated  by  the  instructor  by  means  of  globes,  if 
access  to  them  can  be  obtained,  or  by  such  sensible  objects    ] 
as  he  can  prepare  for  the  purpose.  I 

LESSON  45. 

J 

Day  and  Night.  Fig.  40.     If  the  line  N  S,  which  repre-  \ 

sents  the  axis  of  the  earth,  were  always  in  the  circle  that  j 

divides  the  light  hemisphere  from  the  dark  one,  the  days  and  ; 

nights  would  be  every  where  equal ;  for  an  inhabitant  at  the  i 

equator,  and  one  on  the  same  meridian  towards  the   poles,  i 

would  come  into  the  light  at  the  same  time,  and  immerge  \ 

into  darkness  at  the  same  time.     But  the  line  N  S  is  not  in  \ 

this  circle,  but  has  more  or  less  of  the  positions  as  represented  \ 

at  the  sign  Cancer  or  Capricorn,  that  is,  at  Dec.  23d  or  June  \ 

21st.     Here  it  is  plain  that  an  inhabitant  at  the  equator  does  \ 

not  come  out  of  the  dark   hemisphere  or  immerge  into  it  at  j 

the  same  time  with  an  inhabitant  on  the  same  meridian  to-  \ 

wards  the  poles.     But  while  the  earth  is  at  Capricorn,  an  in-  | 

habitant  on  the  north  side  of  the  equator  is  in  the  light  hemi-  | 
sphere  longer  than  in  the  dark ;  that  is,  the  day  is  longer 

than  the  night.     But  at  Cancer,  an  inhabitant  on  the  north  | 

side  of  the  equator  is  in  the  dark  hemisphere  longer  than  in  \ 

the  light ;  that  is,  the  night  is  longer  than  the  day  :  whereas  j 

at  the  equator,  in  all  situations  of  the  earth,  day  and  night  \ 

are  equal.  1 

LESSON  46.  \ 

Changes  of  the  Seasons.  Fig.  40.     The  variety  of  the  \ 

seasons  depends  (1,)  upon  the  length  of  the  days  and  nights;  j 

and   (2,)   upon  the  position  of  the   earth   with   respect  to  1 

the  sun.     In  what  manner  the  seasons  are  affected  by  the  j 

different  lengths  of  the  days  and  nights  must  be  evident  from  \ 

what  has  been  said  above ;  and  as  to  the  other  circumstance,  \ 

it  is  manifest  from  a  mere  inspection  of  the  figure,  that  in  j 

June  the  sun's  rays  will  fall  more  perpendicularly  upon  an  \ 

inhabitant  on  the  north  side  of  the  equator  than  in  Dec,  for  j 


APPENDIX.  301 

N  is  turned  towards  the  sun  in  June  and  from  it  in  Dec. ; 
it  is  warmer  therefore  at  the  former  season  than  at  the  latter. 
But  to  render  the  subject  more  plain  it  may  be  proper  to 
trace  the  annual  motion  of  the  earth  in  its  orbit.  About  the 
20th  of  March  the  earth  is  in  Libra,  and  consequently  to  its 
inhabitants  the  sun  will  appear  in  Aries,  and  be  vertical  to, 
or  over  the  equator.  The  equator  and  all  its  parallels  are 
then  equally  divided  between  the  light  and  the  dark,  and 
consequently  the  days  and  nights  are  equal  all  over  the 
world.  As  the  earth  pursues  its  journey  from  March  to  June, 
its  northern  hemisphere  comes  more  into  light,  and  on  the 
21st  of  that  month,  the  sun  is  vertical  to  the  tropic  ot  Can- 
cer. All  the  circles  parallel  to  the  equator  are  then  unequal- 
ly divided ;  those  in  the  northern  half  have  their  greater 
parts  in  the  light,  and  those  in  the  southern  have  their  longer 
parts  in  darkness  ;  it  is  summer  therefore  to  the  inhabitants 
of  the  northern  hemisphere,  and  winter  to  the  soutijern. 
Trace  the  earth  now  to  September,  and  the  sun  is  found 
vertical  again  to  the  equator,  and,  of  course,  the  days  and 
nights  are  again  equal.  And  following  the  earth  in  its 
journey  to  Decemi)er,  or  when  it  has  arrived  at  Cancer,  the 
sun  appears  in  Capricorn  ;  and  it  is  vertical  to  that  ^.art  of 
the  earth  called  the  tropic  of  Capricorn,  and  now  the  southern 
pole  is  enlightened,  and  all  the  circles  in  that  hemisphere  have 
their  longer  parts  in  the  light,  and,  of  course,  it  is  summer 
to  those  parts,  and  winter  to  us  in  the  northern  hemiriptiere. 
Note.  Since  it  is  summer  to  all  those  parts  of  the  earth, 
where  the  sun  is  vertical,  and  we  find  the  sun  is  vertical 
twice  in  the  year  to  the  equator,  and  every  part  of  the  globe 
between  the  equator  and  tropics,  consequently  there  are  two 
summers  in  a  year  to  all  those  places ;  and  in  those  parts 
near  the  equator,  they  have  two  harvests  every  year. 

LESSON  48. 

Figures  42  and  43.  The  Tides.  S  the  sun,  M  the  moon, 
E  the  earth,  represented  as  covered  with  water.  When  the 
waters  at  c  fig.  42,  are  under  the  moon,  they  will  b  heaped 
up  at  c,  and  recede  from  the  intermediate  points  a  and  &, 
and  being  less  attracted  on  the  opposite  side  will  be  heaped 
up  also  at  d.  The  sun  tends  to  raise  tides  at  a  and  6,  but 
its  only  effect  is  to  diminish  those  of  the  moon.  In  fig , 
26 


303  APPENDIX. 

43,  both  the  moon  and  sun  tend  to  raise  tides  at  the  same 
places  as  at  a  and  h, 

LESSON  49. 

Eclipses,  j/J'^Mrcs  44,  and  45,  Engr.  VI.  Fig.  45,  repre- 
sents an  eclipse  of  the  moon.  A  F  and  B  G  are  two  straight 
lines  drawn  from  the  opposite  parts  of  the  solar  disk,  touch- 
ing the  surface  of  the  earth  at  C  and  D.  The  moon  m  is 
seen  passing  through  the  earth's  shadow  in  opposition  to  the 
sun.  Besides  the  dark  shadow  of  the  earth,  C  F  D  G  which 
would  terminate  in  a  point  if  continued  far  enough,  there  is 
another  shadow  C  r  s  D,  distinct  from  the  former  and  called 
the  penumbra,  which  is  faint  at  the  edges  towards  r  and  S 
but  becomes  darker  towards  F  and  G.  The  instant  the 
moon  enters  the  earth's  shadow  at  x,  it  is  deprived  of  the 
sun's  light,  and  is  eclipsed  to  all  in  the  illuminated  hemi- 
sphere of  the  earth.  As  the  shadow  of  the  earth  is  but  a  little 
darker  than  the  region  of  the  penumbra  next  it,  it  is  difficult 
to  determine  the  exact  time  when  the  moon  passes  from  the 
penumbra  into  the  shadow,  and  from  the  shadow  into  the 
penumbra,  that  is,  when  the  eclipse  begins  and  ends.     Fig- 

44,  represents  an  eclipse  of  the  sun.  As  the  sun  constantly 
illuminates  half  the  earth's  surface,  and  as  the  moon's  shadow 
falls  upon  but  a  part  of  this  illuminated  hemisphere,  the  sun 
therefore  appears  eclipsed  to  but  a  part  of  those  to  whom  he 
is  visible.  Sometimes  when  the  moon  is  at  its  greatest  dis- 
tance, its  shadow  o  m  terminates  before  it  reaches  the  earth, 
and  then  to  an  inhabitant  directly  under  the  point  o,  the 
eclipse  will  appear  annular.  The  other  shadow  C  r  s  D  is 
the  penumbra.  Within  the  dark  shadow,  the  sun  is  totally 
eclipsed,  but  within  the  penumbra,  only  a  part  of  the  sun's 
rays  are  intercepted,  and  the  sun  is  partially  eclipsed.  The 
beginning  and  ending  of  a  solar  eclipse  may  be  determined 
instantaneously.  The  penumbra,  under  the  most  favourable 
circumstances,  falls  upon  but  about  half  of  the  illuminated 
hemisphere  of  the  earth.  Note.  The  pupil  should  be  taught 
to  enlarge  the  above  as  well  as  other  explanations  of  the 
figures. 

LESSON  60.  Caloric. 
Different  kinds  of  Thermometers.     Fahrenheit's  thermo- 
meter is  universally  used  in  Great  Britain,  and  for  the  most 


APPENDIX.  303 

part  throughout  the  United  States.  In  it,  the  range  between 
the  freezing  and  boiling  points  of  water  is  divided  into  180 
degrees ;  and  as  the  greatest  possible  degree  of  cold  was 
then  supposed  to  be  that  produced  by  mixing  snow  and  com- 

Imon  salt,  it  was  made  the  zero,  or  commencement  of  the 
^6cale,  hence  the  freezing  point  became  32°  and  the  boiling 
^point  212°.  Reaumer's  thermometer,  which  was  formerly 
«sed  in  France,  divides  the  space  between  the  freezing  and 
^boiling  of  water  into  80°,  and  places  the  zero  at  the  freezing 
-point.  The  Centigrade  thermometer  places  the  zero  at  the 
freezing  point,  and  divides  the  range  between  it  and  the 
boiling  point  into  100°.  This  has  long  been  used  in  Swe- 
den under  the  title  of  Celsius's  thermometer.  Dc  Lisle' s 
thermometer  is  used  in  Russia.  The  graduation  begins  at 
the  boiling  point,  and  increases  towards  the  freezing  point. 
The  boiling  point  is  marked  0  and  the  freezing  point  150* 


LESSON  65. 

\mple  Combustibles.  The  following  is  an  enumeration  and 
■  classincatioa  of  the  simple  bodies  in  general.  I.  Compre- 
"hending  the  imponderable  agents,  Heat  or  Caloric,  Light,  and 
Electricity.  II.  Comprehending  agents  capable  of  uniting 
with  inflammable  bodies,  and  in  most  instances  of  effecting 
their  combustion, — Oxygen,  Chlorine,  and  Iodine.  Many 
learned  chemists  have  doubted  whether  Chlorine  and  Iodine 
were  supporters  of  combustion,  any  farther  than  they  contain 
oxygen.  They  are  classed  among  the  simple  bodies  because 
they  have  not,  as  yet,  been  resolved  into  other  ingredients. 
The  name  chlorine  is  simply  expressive  of  its  greenish  colour, 
and  iodine  of  its  violet  colour.  III.  Comprehending  bodies 
capable  of  uniting  with  oxygen,  and  forming  with  it  various 
compounds, — 1.  Hydrogen,  forming  water.  2.  Bodies  form- 
ing acids.  Nitrogen,  forming  nitric  acid.  Sulphur,  forming 
sulphuric  acid.  Phosphorus,  forming  phosphoric  acid.  Car- 
bon, forming  carbonic  acid.  Boron,  forming  boric  acid. 
Fluorine,  forming  fluoric  acid.  3.  Metallic  bodies,  which 
have  been  divided  into  the  seven  following  classes.  1st. 
The  metals  which  combine  with  oxygen  and  form  alkalies. 
These  are  potassium,  sodium,  and  lithium.  The  volatile  al- 
kali ammonia  has  been  found  by  Sir  H.  Davy  to  be  a  triple 


304 


APPENDIX. 


compound  of  nitrogen,  hydrogen,  and  oxygen.  2d.  Those 
metals  which  by  combining  with  oxygen  form  the  alkaline 
earths;  viz.  calcium,  magnesium,  barium,  and  strontium. 
Calcium  is  the  base  of  lime,  magnesium  of  magnesia,  and  so 
on.  These  metallic  substances  are  of  the  colour  of  silver. 
3d.  Those  metals  which  by  combining  with  oxygen  consti- 
tute the  remainder  of  the  earths.  These  are  silicum,  alu- 
mium,  zirconium,  glucinum,  yttrium,  and  thorinum.  These 
are  presumed  metals,  for  the  earths,  of  which  they  are  sup- 
posed to  constitute  the  bases,  have  been  as  yet  but  partially 
decomposed  :  respecting  some  of  them  little  is  known.  4th. 
The  metals  which  absorb  oxygen  and  decompose  water  at  a 
high  temperature.  These  are  iron,  tin,  zinc,  cadmium,  and 
manganese.  5th.  Those  metals  which  absorb  oxygen  at 
different  temperatures,  but  do  not  decompose  water  at  any 
temperature.  This  class  is  composed  of  twelve  distinct 
metals,  viz.  osmium,  cerium,  tellurium,  titanium,  uranium, 
nickel,  cobalt,  copper,  lead,  antimony,  bismuth,  and  mercury. 
6th.  Those  metals  which  do  not  decompose  water,  but  ab- 
sorb oxygen,  and  are  thereby  converted  into  acids.  These 
are  arsenic,  molybdenum,  tungsten,  chromium,  columbium,  and 
selenium.  7th.  The  metals  which  do  not  decompose  water, 
nor  absorb  oxygen  from  the  atmosphere  at  any  tempera- 
ture. These  are  platina,  gold,  silver,  palladium,  rhodium, 
and  iridium. 

LESSON  m. 

A  Retort,  Jig.  48,  Engr.  VI.  A  vessel  in  the  shape  of  a 
pear,  with  its  neck  bent  downwards,  used  in  distillation.  The 
extremity  of  the  neck  may  be  fitted  into  another  glass  ves- 
sel, called  a.  receiver.  Fig.  48,  represents  a  common  glass 
retort,  an  instrument  much  used  in  chemical  laboratories  for 
various  purposes.  A  tubulated  retort  is  an  instrument  like 
the  latter,  with  a  tube  at  the  bend  T,  and  with  a  ground  glass 
stopper  to  fit  it.  This  is  the  most  useful  kind  of  retort,  as 
materials  may  be  put  in  through  the  tube  during  the  opera 
tion.  The  student  may  find  engravings  and  descriptions  of 
a  chemical  apparatus  in  Parkes'   Rudiments  of  Chemistry. 

Note.  Chlorine  may  be  procured  by  heating  in  a  glass 
retort  a  mixture  of  equal  weights  of  the  black  oxyd  of  man- 
ganese and  common  muriatic  acid  (spirit  of  salt.)     The  gas 


APPENDIX.  305  '\ 

is  soon  liberated,  and  may  be  conveniently  collected  over  { 
warm  water.  The  attraction  of  chlorine  for  the  metals  is  in  i 
most  instances  extremely  energetic  :  when  copper  leaf,  or  j 
antimony,  or  arsenic  in  powder,  are  thrown  into  the  gas,  they  ; 
immediately  enter  into  vivid  combustion  and  form  binary 
compounds.  Upon  the  French  theory  of  combustion,  oxy-  ; 
gen  is  absolutely  necessary  to  the  phenomena,  but  here  are  in-  | 
stances  of  brilliant  inflammation  without  the  presence  of  that  \ 
body  (that  is  if  chlorine  be  a  simple  substance,  containing  .; 
no  oxygen.)  Other  cases  might  be  adduced,  such  as  the  ,! 
combustion  which  ensues  when  copper  filings  and  sulphur  1 
are  heated  together  in  an  exhausted  vessel,  or  when  potas-  ; 
sium  and  arsenic  are  made  to  combine  under  similar  circum-  i 
stances.  Comb'istion  therefore  is  to  be  regarded  as  the  ] 
general  result  of  the  exertion  of  powerful  chemical  attraction,  1 
and  not  as  dependent  upon  any  peculiar  substance,  or  as  r^  ■ 
suiting  from  the  decomposition  of  any  distinct  form  of  matter. 
When  phosphorus  is  introduced  into  chlorine,  it  sponta-  \ 
neously  ignites  and  burns  with  a  pale  yellowish  flame,  pro-  | 
ducing  a  white  volatile  substance,  composed  of  two  proper-  j 
tions  of  chlorine  and  one  of  phosphorus.  \ 

LESSON  67.  i 

Electrical  Mac1iine,jig.  49.  A  the  glass  cylinder. — B  the  i 
prime  conductor. — R  the  rubber,  or  cushion. — C  the  chain,  j 

LESSON  68.  ! 

Ley  den  Phial,  Jig.  50.  A  a  round  brass  ball  at  the  ex-  : 
tremity  of  a  wir'e,  which  passes  through  a  cork  D.  R  is  a  ^^ 
discharging  rod, — a  a  two  brass  knobs  or  balls  attached  to  • 
wires  which  are  fastened  to  the  handle  at  x. 

LESSON  70.  1 

Voltaic  pile,  Jig.  47.  The  pieces  of  copper,  zinc,  and  : 
woollen  cloth,  are  supported  with  three  rods  of  glass,  as  a  6,  ; 
ah,  ah,  and  pieces  of  wood  x  and  z.  ^ 

\ 
LESSON  7L  I 

Fig.  46.  A  B  a  trough  made  of  baked  wood. — w  w  ar©^  \ 
wires  fastened  to  pieces  of  copper  and  put  into  the  outer  cells/  ^ 


306  ApPENDrx. 

— a  a  are  little  glass  tubes  to  hold  the  wires  by, — v  is  a  glass 
plate  on  which  the  ends  of  the  wires  are  to  be  brought  to- 
gether. 

LESSON  76. 

Mineralogy.  Werner  divides  the  external  characters  of 
minerals  into  two  kinds,  namely,  general  and  particular. 
The  general  characters  are  the  following:  1.  Colour;  2. 
Cohesion  ;  3.  Unctuosity  ;  4.  Coldness  ;  5.  Weight ;  6.  Smell ; 
7.  Taste.  The  particular  characters  are  the  following:  1. 
Aspect  of  the  surface;  2.  Aspect  of  the  fracture;  3.  Aspect 
of  the  distinct  concretions ;  4.  General  aspect ;  5.  Hard- 
ness ;  6.  Tenacity  ;  7.  Frangibility  ;  8.  Flexibility ;  9.  Ad- 
hesion to  the  tongue  ;   10.  The  sound. 

General  Characters.  I.  The  colours  of  minerals  are  ex- 
tremely various.  Werner  conceives  eight  fundamental  co- 
lours, and  describes  all  the  others  as  compounds  of  various 
proportions  of  these.  The  fundamental  colours  are,  1.  Snow 
white.  2.  Ash  grey.  3.  Velvet  black.  4.  Berlin  or  Prus- 
sian blue.  5.  Emerald  green.  G.  Lemon  yellow.  7.  Car- 
mine red.  8.  Chestnut  brown.  II.  With  respect  to  cohe- 
sion, minerals  are  either  solid,  f?'i able,  or  fluid.  III.  With 
respect  to  unctuosity ,v[\mexs\s2Lxe  distinguished  mio  greasy, 
and  meagre ;  the  first  have  a  certain  degree  of  greasiness  in 
the  feel ;  the  second  not.  The  other  four  general  charac- 
ters require  no  particular  description. 

Particular  characters.  I.  In  the  aspect  of  the  surface  of 
■  a  mineral,  three  things  claim  attention.  L  The  shape  of 
the  mineral.  2.  The  kind  of  surface.  3.  The  lustre  of  the 
surface,  which  is  either  splendent,  shining,  glistening,  glim- 
mering, or  dull.  II.  When  a  mineral  is  broken,  the  new 
surface  exposed  is  called  the  fracture.  Three  things  claim 
attention:  1.  The  lUstre  of  the  fracture.  2.  The  kind  of^ 
fracture.  3.  The  shape  of  the  fragments.  III.  Distinct 
concretions  are  distinct  masses,  which  may  be  separated  from 
each  other,  without  breaking  through  the  solid  part  of  the 
mineral,  by  natural  seams.  Three  particulars  with  respect 
to  these  are,  1.  Their  shape.  2.  Their  surface,  3.  Their 
lustre.  IV.  Under  the  headof  ^ener«/  aspect,  three  particu- 
lars are  comprehended,  1.  The  transparency .  2.  The  streak. 
3.  The  soiling,  or  the  stain  left  when  rubbed.    V.  Minerals 


APPENDIX.  307 

are  either,  I,  Hard.  2.  Semihard,  or,  3.  Soft.  VI.  With 
respect  t*o  Tenacity,  minerals  are,  1.  JBrittle,  when  on  being 
cut  with  a  knife  the  particles  fly  away  with  noise ;  2.  Sectile, 
when  the  particles  do  not  fly  off  but  remain ;  3.  Ductile, 
when  the  mineral  can  be  cut  into  slices.  VIJ.  By  Frangi- 
hility  is  meant  the  resistance  which  minerals  make  when 
we  attempt  to  break  them.  The  degrees  are  five,  1.  Very 
tough ;  2.  Tough ;  3.  Moderately  tough ;  4.  Fragile ;  5. 
Very  fragile.  VIII.  With  respect  to  Flexibility,  some  are, 
.  1.  Elastic;  others,  2.  Common;  others,  3.  Injlexible.  IX. 
Some  minerals  adhere  to  the  tongue,  1.  Very  strongly  ;  2. 
others  moderately ;  3.  others  slightly ;  4.  and  others  very 
slightly.  X.  Some  minerals  give  a  ringing  sound  ;  others 
a  grating  sound  ;  others  a  creakiug  sound,  as  tin. 

With  respect  to  electricity,  some  fninerals  become  electric 
when  heated,  others  when  rubbed,  others  cannot  be  rendered 
electric.  The  electricity  of  some  is  positive,  of  others  nega' 
tive. 

LESSON  79. 

Silver  and  Mercury.  Freezing  mixtures.  Salts  dissolved 
in  water,  ice,  or  snow  dissolved  in  nitric  and  muriatic  acids, 
reduce  the  temperature  of  the  mixtures  a  great  number  of 
degrees.  Mercury  has  been  frozen  or  rendered  solid,  even 
in  summer,  bough  it  requires  the  temperature  of  39°  below 
zero  at  least  .o  congeal  that  metal.  Four  parts  of  caustic 
potash,  crystallized,  and  reduced  to  a  fine  powder,  mixed  with 
three  parts  ofsnow  sinks  the  mercury  in  a  thermometer  from 
32^  above  to  51°  below  zero.  Two  parts  muriate  of  lime 
mixed  with  one  of  snow,  sinks  it  from  zero  to  66°  below 
zero.  The  cause  is,  that  the  mixture  has  a  larger  capacity 
for  caloric  than  would  be  derived  from  blending  the  two  ca- 
pacities  of  the  ingredients,  and  taking  a  mean  proportional 
between  them. 

LESSON  91. 

Roots,  Stems,  Buds  and  Leaves.  The  generality  of  roota^ 
may  be  arranged  under  the  following  heads.  1.  A  Fibrous 
Root,  consisting  only  of  fibres  either  branched  or  undivided. 
Many  grasses  and  the  greater  part  of  annual  herbs  have  this 
4tind  of  root.    2.  A  Creeping  Rootf  as  in  Mint.    3.  A  Spin^ 


308 


APPENOrX, 


die-shaped  or  Tapering  Root,  as  the  Carrot,  Parsnip,  and 
Red  Clover.  4.  An  Abrupt  Root,  is  naturally  inclined  to 
the  last  mentioned  form,  but  from  some  decay  or  interruption 
in  its  descending  point,  it  becomes  abrupt,  or  as  it  were  bit- 
ten off.  It  is  found  in  many  of  our  native  Violets.  5.  A 
Tuberous  or  Knobbed  Root,  is  of  many  different  kinds,  as  in 
the  Potatoe  and  the  Artichoke.  Several  of  the  Pea  kind 
are  furnished  with  them  on  a'smaller  scale.  6.  A  Bulbous 
Root,  is  either  solid,  as  in  the  Crocus  ;  tunicate,  composed 
of  concentric  layers,  as  in  the  onion;  or  scali/,  like  that  of 
the  Lily.  7.  A  Jointed  or  Granulated  Root,  as  in  the  Wood 
Sorrel  and  White  Saxifrage.  It  is  evident  that  fleshy  roots, 
whether  of  a  tuberous  or  bulbous  nature,  must  at  all  times 
powerfully  resist  the  drought.  The  common  herdsgrass,  or 
Timothy,  when  growing  in  pastures  that  are  uniformly  moist, 
has  a  fibrous  root,  but  in  dry  situations,  it  acquires  a  bulbous 
one.  This  is  an  evident  provision  of  nature  to  guard  the 
plant  against  too  sudden  a  privation  of  moisture  from  the 
soil. 

The  seven  kinds  of  stems  are  as  follows.  \.  Caulis,  a  ste7n 
properly  so  called,  which  bears  or  elevates  from  the  root,  the 
leaves  or  flowers.  The  trunks  and  branches  of  all  trees  and 
shrubs  come  under  this  denomination,  as  well  as  of  a  greater 
proportion  of  herbaceous  plants.  2.  Culmus,  a  straw  or 
culm,  is  the  peculiar  stem  of  grasses,  rushes,  and  plants  near- 
ly allied  to  them.  3.  Scapus,  a  stalk,  springs  from  the  root, 
and  bears  the  flowers  and  fruit,  but  not  the  leaves,  as  in  the 
Primrose  and  Cowslip.  4.  Pedunculus,  the  Flotoer-stalk, 
springs  from  the  stem,  and  bears  the  flowers  and  fruit,  but 
not  the  leaves.  5.  Petiolus,  the  Foot-stalk,  or  Leaf-stalk, 
This  term  is  applied  exclusively  to  the  stalk  of  a  leaf  6. 
Frons.  A  Frond.  In  this  the  stem,  leaf,  flowers,  and  fruit 
are  produced  from  the  leaf  itself  as  in  the  Fern  tribe.  7. 
Stipes,  Stipe,  is  the  stem  of  a  frond,  which  in  ferns  is  com- 
monly scaly. 

Botanists  enumerate  above  100  distinctions  of  leaves,  ac- 
cording to  their  position  and  form. 

There  are  several  kinds  of  appendages  to  a  plant  which 
were  not  mentioned  in  any  of  the  Lessons  on  Botany.  1. 
Stipula,  Stipule,  a  leafy  appendage  to  the  proper  leaves  or  to 
their  footstalks.  They  are  usually  found  in  pairs  at  the  base 
of  the  petiole.    In  the  common  Pea  they  are  round,  and  in 


APPENDIX.  309 

Other  plants  they  assume  other  figures.  In  the  natural  order 
of  Grasses  it  is  solitary,  forming  a  membranous  scale,  which 
arises  from  the  summit  of  the  sheath,  and  like  it  encloses 
the  culm.  2.  Bractca,  The  Floral  Leaf^  a  leafy  appendage 
to  the  flower  or  its  stalk.  It  is  of  a  variety  of  forms.  3.  Spi- 
na, a  thorn,  which  proceeds  from  the  wood  itself.  4.  AcU' 
leus,  a  prickle,  arises  from  the  bark  only  and  comes  off  with 
it.     5.  Cirrus,  a  tendril.     This  is  intended  solely  to  sustain 

■  weak  and  climbing  stems  upon  more  firm  and  sturdy  ones. 
Tendrils  or  claspers  when  young  are  usually  put  forth  in  a 
straight   direction ;    but  they  presently  become   spiral.    6. 
Glandula,  a  gland,  a  little  tumour  discharging  a  fluid.  They 
occur  in  the  substance  of  the  leaves  of  the  Myrtle,  Lemon, 
and  common  St.  John's  Wort.    7.  Pilus,  a  hair.     This  is  an 
,jgi,  excretory  duct  of  a  bristle  like  form.     In  the  Nettle  it  is  tu- 
■■  bular  and  pervious,  having  each  a  bag  of  poison  at  its  base, 
^klike  the  fang  of  a  serpent.     But  the  hairs  which  clothe  many 
^Kplants  are  merely  a  protection  against  cold,  heat,  or  insects. 
^Kt'-    The  several  kinds  of  Inflorescence,  or  modes  of  flowering 
^B>are  as  follows.    1.  The  Umbel,  a  number  of  flower  stalks  is- 
^B  suing  from  a  common  centre,  diverging  like  the  rays  of  an 
I^R'Umbrella,  bearing  their  flowers  on  the  summit,  and  raising 
^^^  them    about  the  same  height.     The    Carrot,   Parsnip,  and 
Hemlock  are  familiar  examples,  which,  with  all  others  like 
them  in  this  respect,  are  called  umbelliferous  plants.    2.  A 
Cyme  has  the  general  appearance  of  an  umbel,  and  agrees 
with  it  so  far  that  its  common  stalks  all  spring  from  one  cen- 
tre, but  differs  in  having  those  stalks  variously  and  alternate- 
ly subdivided,  as  in  the  Elder  and  other  species  of  Viburnum. 
3.    A  Corymb  is  a  spike  whose   partial  flower    stalks    are 
gradually  longer  as  they  stand  lower,  so  that  all  the  flowers 
are  nearly  on  a  level.     The  flowers  of  Yarrow  grow  in  this 
manner.    4.  A  Fascicle  is  an  assemblage  of  flowers  more 
densely  arranged  than  in  the  Corymb,  as  in  the  Sweet- Will- 
iam.    5.  A  Spike  is  an  assemblage  of  flowers  arising  from 
the  sides  of  a  common  stem,  as  in  the  herdsgrass.     The 
flowers  are  commonly  all  crowded  close  together,  but  some- 
times they  form  separate  groups,  as  in  some  Mints.    6.  A 
Raceme,  or  cluster,  as  in  the  Currant.    7.  A  Head,  or  Tuft, 
(capitulum)  is  an  assemblage  of  flowers  ijpon  the  extremity 
of  the  branch  or  stem,  and  arranged  in  a  globular,  oval  or 
cylindrical  form,  as  in  the  Globe  Amaranth,  and  in  several 


310  APPENDIX. 

species  of  Clover.  8.  A  Whorl  ( Verticillus)  is  an  assem- 
blage of  flowers  surrounding  the  stem  or  its  branches,  as  in 
the  Dead  Nettle  and  Mint.  9.  A  Panicle  bears  the  flowers 
in  a  sort  of  loose  subdivided  bunch  or  cluster,  without  any 
order,  as  in  the  Oat.  10.  A  Thyrse  is  a  dense  or  close  pani- 
cle, more  or  less  of  an  ovate  figure,  of  which  the  Lilac  is 
an  example. 

LESSON  92. 

FUwer  and  Fruit.  The  Calyx,  Flower-cup,  or  Empale- 
ment,  as  it  is  sometimes  called,  is  divided  into  seven  kinds.  1. 
A  Cup,  {Perianthum)  properly  so  called,  as  in  the  five  green 
leaves  which  encompass  a  Rose.  2.  A  Fence,  {Involucrum) 
as  in  the  Hemlock  or  Carrot.  3.  A  Catkin  (Amentum)  as 
in  the  Willow  or  Hazel.  4.  A  Sheath,  (Spatha)  as  in 
the  Snow-drop  or  Narcissus.  The  Spatha  sometimes  en- 
closes a  Spadix,  or  elongated  receptacle,  as  in  Dragon-root. 
In  Indian  corn,  the  spadix  is  enclosed  by  leaves  or  husks ; 
in  the  Sweet  Flag,  it  is  naked.  5.  A  Husk,  (Gluma)  as  in 
oats,  wheat,  or  grasses.  6.  A  Veil,  or  scaly  sheath^  (Peri- 
chaetium)  as  in  some  mosses.  7.  A  Cap,  or  Wi-apper, 
{Volva)  as  in  mushrooms. 

The  seed-vessel  [Pericarpium)  is  also  divided  into  seven 
kinds.  1.  A  Capsule,  as  in  the  poppy.  2.  A  Vodi,  {Siliqua) 
as  in  wall-flower  and  honesty.  3.  A  Legume,  or  Shell,  as  in 
pea  and  broom.  4.  Drupe,  as  in  cherry  and  peach.  5.  A 
Berry,  (Bacca)  as  in  elder  and  gooseberry.  6.  A  Pome,  as 
in  apple  and  pear.  7.  A  Cone,  [Strobilus)  as  in  fir  and 
pine. 

A  Seed  is  composed  of  several  parts.  Embryo,  or  germ 
called  by  Linnaeus  Corculum,  or  little  heart.  The  Cotyle- 
dons or  seed-lobes,  immediately  attached  to  the  embryo. 
Albumen,  or  the  White,  a  farinaceous  substance  to  nourish 
the  germinating  embryo.  The  Yolk,  ( Vitellus)  less  general 
than  the  other  parts  already  mentioned,  but  absorbed,  like 
the  albumen,  for  the  nourishment  of  the  embryo.  The 
Skin  ( Testa)  contains  all  the  parts  of  a  seed  above  described, 
giving  them  their  due  shape.  The  Scar,  (Hilum)  the  point 
by  which  the  seed  is  attached  to  the  seed-vessel,  or  recepta- 
cle. The  Pellicle,  closely  adhering  to  the  outside  of  some 
seeds,  so  as  to  conceal  the  proper  colour  and  surface  of  their 


APPENDIX.  311 

skin.  The  Tunic,  (arillus),  a  complete  or  partial  covering  of 
a  seed,  fixed  to  its  base  only,  and  more  or  less  loosely,  or  close- 
ly enveloping  its  other  parts.  The  Seed-down,  (Pappus,)  the 
chaify,  feathery,  or  bristly  crown  of  many  seeds  that  have  no 
Pericarp.  Its  use  is  to  transport  seeds  from  their  native 
spot,  as  in  the  Thistle,  and  Dandelion.  The  Tail,  (Cauda,) 
formed  from  the  permanent  style,  and  generally  of  a  feathery, 
hairy  appearance.  Beak,  (Rostrum,)  an  elongation  of  the 
seed-vessel,  though  applied  to  some  naked  seeds.  A  Wing 
(Ala)  is  a  membranous  appendage  to  seeds,  or  their  cap- 
sules. The  Awn  is  usually  an  appendage  to  the  flower  and 
seeds  of  grasses  Seeds  are  occasionally  furnished  with  spines, 
hooks,  scales,  «fec.,  designed  for  their  security  while  living, 
and  for  their  subsequent  dispersion. 


H|  and  i 

L 


LESSON  93. 


Table  of  the  24  Classes. 

1.  Monandria 1  Staanen.  Pigeon's  foot  and  Star  wort. 

2.  Diandria 2  stamens.  Pennyroyal,  Lilac. 

3.  Triandria 3  do.        Blue  flag,  tierdsgrass. 

4.  Tetrandria ...  4  do.        Chequer  berry.  Witch  hazel. 

5.  Pentandria  ...  5  do.        Swamp  Pink,  Midlein,  Violet, 

6.  Hexandria ...  6  do.        Barberry,  Lily,  Sweet  Flag. 

7.  Heptandria  .  .  7  do.        Horse  chestnut. 

8.  Octandria  ...  8  do.         Blue  berry,  Crane  berry. 

9.  Enneandria . .  9  do.        Sassafras,  Fever  bush. 

10.  Decandria.  . .  10      do.        Ground  Laurel,   Chickweed, 

Pink. 

11.  Dodecandria.l2     do.        Purslane,  Wild  Ginger. 

12.  Icosandria. .  .  20      do.  or  more,  inserted  into  the  Calyx. 

Rose. 

13.  Polyandria. . .  Many  Stamens,  inserted  into  the  recepta- 

cle.   Buttercups. 

14.  Didynamia. . .  4    Stamens :  2  long  and  2  short.     Spear- 

mint, Catmint. 

15.  Tetradynamia  6         do.       4  long  and  2  short.  Mustard. 

16.  Monadelphia.  Filaments  united  at  bottom,  but  separate 

at  top.     Mallow. 

17.  Diadelphia  .  .  Filaments  in  two  sets.  Fumitory,  Lupine. 

18.  Polyadelphia .  Filaments  in  many  sets.   St.  John's  Wort. 


312  APPENDIX. 

19.  Syngenesia ..  Anthers  united  into  a  cylinder;  flowers 

compound. 

20.  Gynandria. . .  Stamens    and    pistils    together.     Ladies^ 

Slipper. 

21.  MoncEcia ....  Stamens  and   pistils  in  separate  flowers, 

upon  the  same  plant.     Nettle. 

22.  DioBcia Stamens  and  pistils  in  separate  flowers, 

upon  different  plants.     Hop. 

23.  Polygamia  . .  Variously  situated. 

24.  Cryptogamia.  Flowers  inconspicuous. 

The  names  of  the  classes,  which  at  first  sight  appear  dif- 
ficult, are  formed  of  Greek  words,  expressive  of  the  charac- 
ters of  each  class ;  and  those  of  the  first  ten  classes  may  be 
easily  remembered,  by  considering  the  word  andria,  as 
meaning  the  same  as  stamens,  and  annexing  it  to  the  Greek 
numerals. 

The  names  of  the  orders,  like  those  of  the  classes,  are 
formed  from  the  Greek  numerals,  but  with  the  addition  of 
the  word  gynia,  instead  of  andria ;  so  that  when  there  is 
but  one  pistil,  the  plant  is  said  to  be  in  the  order  monogy- 
nia ;  if  there  are  two,  digynia,  &/C. 

Names  of  the  Orders  of  Jir^t  13  Classes. 

Monogynia 1    pistil. 

Digynia 2    pistils. 

Trigynia 3      do. . 

Tetragynia 4      do. 

Pentagynia 5      do. 

Hexagynia 6      do. 

Heptagynia 7      do. 

Octagynia 8     do. 

Enneagynia 9      do. 

Decagynia  ......  10    do. 

Dodecagynia 12    do. 

Polygynia Many  pistils. 

The  14th  class  has  only  two  orders ;  gymnospermia,  in 
which  the  seeds  are  naked  at  the  bottom  of  the  calyx ;  and 
angiospermia,  in  which  they  are  enclosed  in  a  seed  vessel. 
Examples  of  the  first  are  spearmint,  motherwort,  and  catmint, 
and  of  the  second,  cow-wheat,  toad-flax,  and  beech-drops. 


APPENDIX.  313 

The  two  orders  of  the  15th  class  are  distinguished  by  the 
form  of  the  fruit ;  the  first,  called  siliculosa,  has  broad  short 
pods,  as  in  pepper-grass  or  wild-cress  ;  and  the  second,  called 
siliquosa,  is  known  by  its  long  pods,  as  in  wild  radish  and 
common  mustard.  The  orders  of  the  16th,  17th,  and  18th 
classes,  are  characterized  by  the  number  of  stamens  in  each 
flower,  and  the  names  of  some  of  the  classes,  therefore,  are 
used  to  distinguish  them,  as  Triandria,  Decandria,  Polyan- 
dria,  &c.  The  19th  class  has  five  orders,  1st,  cequalis,  all 
the  florets  with  stamens  and  pistils,  and  all  fertile  ;  as  dan- 
delion, burdock,  and  cotton  thistle :  2d,  superflua,  florets  of 
the  disk,  or  surface  with  stamens  and  pistils,  those  of  the 
margin  with  pistils  only,  all  fertile,  as  common  life-everlast- 
ing, white  weed,  and  elecampane  :  3d,  frustanea,  florets  of 
the  centre  with  stamens  and  pistils,  fertile ;  those  of  the 
margin  with  pistils  only,  barren,  as  the  sunflower  :  4th,  ne- 
cessaria,  florets  of  the  centre  with  stamens  and  pistils,  bar- 
ren ;  those  of  the  margin  with  pistils  only,  fertile,  as  what  is 
called  high  water  shrub,  growing  about  the  borders  of  salt 
marshes  :  5th,  segregata,  comprehends  such  flowers  as  have 
tubular  florets,  all  perfect,  each  floret  having  its  own  sepa- 
rate calyx,  in  addition  to  the  general  calyx,  which  includes 
all  the  florets,  as  the  globe-thistle.  The  orders  of  the  20th, 
21st,  and  22d  classes  are  distinguished  by  the  number  of  sfa- 
mens.  The  23d  class  has  three  orders,  1  st,  monmcia,  barren, 
fertile,  and  perfect  flowers,  found  in  one  plant,  as  poke  root, 
or  American  hellebore  :  2d,  dicEcia,  barren,  fertile,  and  per- 
fect flowers  on  different  plants,  as  ginseng,  swamp  maple,  rock 
maple,  and  white  ash  :  3d,  tricucia,  the  same  on  three  sepa- 
rate plants ;  of  this,  the  figtree  is  supposed  to  be  a  solitary, 
though  doubtful  example.  The  24th  class  has  5  orders, 
Filices,  Ferns  ;  Musci,  Mosses;  Hepaticce,  Liverwort;  AlgcB, 
Flags ;  Fungi,  Mushrooms.  The  term.  Algae,  was  original- 
ly applied  to  marine  plants,  as  sea- weeds,  but  it  has  been, 
employed  in  a  more  extensive  sense,  and,  among  others,  em- 
braces the  Lichens  which  cling  to  rocks.  Note.  The  21st, 
22d,  and  23d  classes  have  been  abolished  by  some  writers. 

The  instructer  should  read  and  explain  to  his  pupils  the 
names  of  the  classes  and  orders,  and  point  out  the  circum- 
stances on  which  their  distinctions  are  founded,  by  the  help 
.of  engravings,  or  real  specimens. 

It  may  be  proper  to  give  an  example  of  the  division  of 
27 


1514  APPENDIX. 

classes,  orders,  genera,  and  species.  The  geranium,  from 
its  having  ten  stamens  united  in  one  set,  is  in  the  class 
Monadelphia,  and  order  Decandria  :  the  whole  family  of  the 
plant  geranium  constitutes  a  genus  of  the  order  above  men- 
tioned ;  and  the  different  kinds,  as  ivy-leaved,  rose-scented, 
spotted  (or  Cranesbill,)  vi^ood  geranium,  &/C.  are  the  different 
species  of  the  genus. 

To  distinguish  the  species  of  a  plant,  botanists  employ  two 
words  ;  the  first  which  is  called  the  generic  name,  is  common 
to  all  the  species  of  the  same  genus ;  and  the  second,  termed 
the  specijic  name,  is  confined  to  a  single  species.  For  ex- 
ample, rosa  dafnascena,  which  is  the  botanic  name  for  the 
damask  rose,  rosa  is  the  generic  name  applicable  to  the  whole 
genus  or  family  of  roses,  and  damascena  is  the  specijic  name, 
used  to  distinguish  the  particular  kind  or  species  of  rose. 
Rosa  alba,  or  white  rose,  is  another  species.  Sweet  Briar  is 
a  species  of  rose,  called  JRosa  rubiginosa.  The  genus  Rosa 
is  in  the  class  Icosandria,  having  20  or  more  stamens,  in- 
serted on  the  Calyx,  and  in  the  order  Polygynia,  having 
many  pistils. 

The  Lily  is  represented  in  the  upper  part  of  Engr.  VII. 
It  belongs  to  the  class  Hexandria,  order  monogynia,  having 
six  stamens  2i^  c  c  c  c  c  c,  and  one  pistil  as  d.  Its  corolla  is 
composed  of  six  petals,  sls  bbbbbb.  The  Lily  has  no  calyx. 
Fig.  7  is  an  enlarged  view  of  the  pistil ;  g  its  receptacle  or 
base,  and  d  its  style.  Fig.  5  e,  is  the  seed  vessel  or  pericar- 
pium,  with  its  pistil  represented  as  withered.  There  is  an 
enlarged  view  also  af  a  stamen  with  its  filament,  anther,  and 
pollen. 

Figures  1,  2,  3,  4,  represent  a  Geranium  with  several  of 
its  parts  separately  sketched  : — a,  calyx  five  leaved,  and  1, 
the  same  separated  from  the  stem  : — b  bbb,  the  corolla,  com- 
posed of  five  regular  obcordate  petals :  the  petals  are  called 
ebcordate,  because  they  are  heart-shaped  with  the  point  in- 
ward or  downward,  as  may  be  seen  in  b  2,  which  represents 
one  of  the  petals  apart  from  the  rest. — The  nectary  in  the 
spotted  geranium  consists  of  five  glands,  as  iiii  on  the  base 
of  the  longer  filaments,  cccc,  four  which  only  are  repre- 
sented in  fig.  3. — d  4,  a  pistil,  and /its  seed  or  fruit. 

The  bottom  fig.  h  h  represents  the  base,  or  receptacle  of 
the  cotton  thistle ;  it  is  cellular  like  a  honeycomb. 


APPENDIX. 


3ia 


LESSON  95.    Animal  Kingdom. 
I.   Vertebral  Animals. 

1.  Mammalia,  viviparous,  and  nourish  their  young  with 
milk. 

2.  Birds,  oviparous. 

3.  Reptiles,  as  frogs  and  serpents. 

4.  Irishes. 

The  two  first  of  the  above  classes  are  warm  blooded,  and 
the  two  last  cold  blooded. 


II.  Invertebral  Animals. 

5.  Insects. 

6.  Crustacea,  as  the  lobster  and  crab. 

7.  Mollusca,  as  the  oyster,  clam,  and  cuttle  fish. 

8.  Vermes,  or  worms,  as  the  leech,  earth  worm,  and  hair 
worm. 

9.  Zoophytes,  as  the  star  fish,  sponges,  corals,  and  madre- 
pores. 

Note.  According  to  the  Linnaean  arrangement,  which 
will  be  found  in  most  works  that  treat  systematically  of  na- 
tural history,  all  animals  are  divided  into  six  classes,  1.  Mam' 
malia,  %  Birds,  3.  Amphibia,  4.  Fishes,  5.  Insects,  6.  Worms. 


LESSON  96.    Orders  of  Mammalia. 

1.  The  Bimana  or  two  handed  animals.  Man  is  the  only 
example.  He  has  hands  upon  his  superior  extremities  alone. 
He  has  nails  of  a  thin  and  delicate  texture,  which  give  to  his 
thumb  and  fingers  a  wonderful  delicacy  of  touch. 

2.  The  Quadrumana  or  four  handed  animals,  comprising 
apes,  monkeys,  and  baboons.  They  have  hands  upon  all 
four  of  their  extremities,  but  less  perfect  than  those  of  man. 

3.  The  Carnivora  or  carnivorous  animals.  These  have 
no  hands,  but  their  feet  are  furnished  with  claws.  Note. 
These  three  orders  have  all  the  three  kinds  of  teeth,  which 
diifer  however  in  shape  and  strength,  according  to  the  habits 
and  food  of  the  different  species. 


316  APPENDIX. 

4.  The  Rodentia  or  gnawers.  They  have  no  canine  teeth ; 
and  their  claws  are  similar  to  those  of  the  carnivora. 

5.  The  Edentata  or  toothless  animals ;  so  called  because 
they  are  deficient  always  in  the  incisive  teeth,  and  some- 
times have  no  teeth  at  all. 

6.  The  Ruminantia  or  ruminating  animals  are  those  which 
chew  the  cud.  They  are  cloven  footed,  and  have  more- 
over no  incisive  teeth  in  the  upper  jaw. 

7.  The  Pachydermata  or  thick  skinned  animals.  This 
order  includes  a  considerable  variety  of  other  animals  with 
hoofs,  but  which  do  not  ruminate. 

8.  The  Cetacea,  or  animals  of  the  whale  kind,  distinguished 
by  having  no  posterior  extremities,  and  their  anterior  so  con- 
structed as  to  answer  the  purpose  of  fins,  as  whales,  porpoises, 
and  dolphins. 

9.  The  Marsupial  animals  are  distinguished  from  all 
others  by  the  possession,  in  the  female,  of  a  bag  or  pouch 
{marsupium)  on  the  outside  of  the  abdomen,  for  the  purpose 
of  holding  their  young  after  birth.  Note.  Linnaius  divided 
the  class  mammalia  into  seven  orders;  1.  Primates,  oi this 
order  man  was  placed  at  the  head,  and  next  him,  the  ape, 
monkey,  Oran-outang,  and  bat.  2.  Bruta,  as  the  elephant,  ^ 
sloth,  and  ant-eater.  3.  FercB,  as  the  seal,  dog,  cat,  and 
hedge-hog.  4.  GUres,  as  beavers,  mice,  and  hares.  5.  Pe- 
cora,  as  oxen,  sheep,  goats,  and  others.  6.  Belluce,  as  the 
horse,  hog,  and  the  tapir.    7.  Cetce^  as  the  whale  tribes. 

LESSON  97.    Birds.     . 

The  orders  of  Birds  according  to  Linnaeus  are,  1.  Acci* 
pitres.  2.  Piece,  or  the  pie  kind,  as  parrots,  ravens,  crows, 
&,c.  3.  Anseres,  or  the  duck  kind.  4.  Grallce,  or  the  crane 
kind.  5.  GallincB^  or  the  poultry  kind.  6.  Passeres,  or  the 
sparrow  kind. 

LESSON  98. 

Xinnseus  divided  his  class  Amphibia  into  four  orders,  1. 
Reptiles,  as  the  crocodile,  tortoise,  lizard,  frog,  &c.  2.  iSfer- 
pents,  as  the  rattle-snake,  viper,  &/C.  3.  Meantes,  as  the  si- 
ren.   4.  NanteSi  as  torpedoes,  sharks,  &c. 


ff 


APPENDIX.  317 


LESSON  102.     Vermes. 


Linnaeus  divided  Vermes  or  worms  into  five  orders,  1.  In- 
testinal worms,  as  tape  worms,  leeches,  Slc.  2.  Molluscous 
worms,  chiefly  inhabiting  the  sea.  3.  Testaceous  worms,  as 
muscles,  oysters,  snails,  &c.  4.  Zoopliytes,  5.  Infusoria., 
or  animalcules. 

Note.  In  treating  of  any  particular  animal,  naturalists 
are  accustomed  to  designate  it  by  a  name  derived  from  its 
genus  and  species.  This  name  is  comprised  of  two  words ; 
the  first  being  the  name  of  its  genus ;  and  the  second  being 
altogether  arbitrary,  or  else  expressing  some  circumstance 
relating  to  the  colour,  size,  or  residence  of  the  animal,  which 
serves  in  a  degree  to  distinguish  it  from  others.  The  first  is 
called  its  generic,  the  second  its  trivial  or  specific  name. 
For  example :  in  the  class  Mammalia,  order  carnivora,  the 
genus  Felis  includes  all  those  of  the  cat  kind  (Felis  being^ 
the  Latin  word  for  cat)  and  these  animals,  although  differing 
one  from  another  very  much  in  size  and  colour,  have  yet  a 
very  close  resemblance  in  their  general  form,  figure,  charac- 
ter, and  habits  of  life.  The  different  species  of  the  genus 
Felis  are  distinguished  from  one  another  in  the  following 
manner  : — The  Lion  is  called  Felis  leo ;  the  Tiger,  Felis 
tigris ;  the  Leopard,  Felis  leopardus  ;  the  Lynx,  Felis  lynx, 
&c.  In  the  genus  Canis,  the  dog  is  called  Canis  domesti- 
cus  ;  the  wolf  Canis  lupus  ;  the  fox,  Canis  vulpes,  &c.  In 
the  class  of  Birds,  order  accipitres,  the  genus  Falco  includes 
those  of  the  eagle  or  hawk  kind: — The  fierce  eagle  is  called 
Falco  ferox,  the  common  falcon,  Falco  communis,  the  Ameri- 
can brown  hawk,  Falco  fuscus,  &/C. 

The  Lessons  on  Zoology,  in  this  Class  Book,  have  been 
abstracted  from  Dr.  John  Ware's  edition  of  Smellie's  Phi- 
losophy of  Natural  History  ;  chiefly  from  the  Ii^roduction, 
which  was  wholly  prepared  by  Dr.  W.,  whose  system  of  clas- 
sification is  principally  derived  from  Cuvier,  a  celebrated 
French  naturalist.  The  class  of  insects,  however,  is  ar- 
ranged in  orders  according  to  the  system  of  Linnaeus.  Be- 
sides the  above,  the  following  works  have  been  consulted, 
and  from  many  of  them  extracts  made.  Conversations  on 
Natural  Philosophy  ;  Webster's  Elements  of  Natural  Phi- 
losophy ;  Blair's  Grammar  of  Natural  and  Experimental 
27* 


318  APPENDIX. 

Philosophy ;  Blair's  Universal  Preceptor ;  Blair's  Class 
Book;  Joyce's  Scientific  Dialogues,  3  vols.  12mo.  Wil- 
kins'  Elements  of  Astroijomy ;  Parkes'  Rudiments  of 
Chemistry  ;  Conversations  on  Chemistry  ;  Thomson's  Sys- 
tem of  Chemistry,  4  vols.  8vo. ;  Wakefield's  Introduction  to 
Botany  ;  Smith's  Introduction  to  Physiological  and  Syste- 
matical Botany ;  Sumner's  Compendium  of  Physiological 
and  Systematic  Botany ;  Bigelow's  Collection  of  Plants  of 
Boston  and  its  Vicinity ;  Conversations  on  Political  Econo- 
my ;  Rett's  Elements  of  General  Knowledge ;  Paley's 
Natural  Theology ;  Paley's  Moral  Philosophy ;  Brown's 
Lectures  on  the  Philosophy  of  the  Human  Mind ;  Rees' 
Cyclopedia;  Nicholson's  Encyclopsedia ;  North  American 
Review ;  United  States  Literary  Gazette. 


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